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Filed pursuant to Rule 424(b)(5)
Registration No. 333-185599

PROSPECTUS SUPPLEMENT
(To Prospectus dated January 8, 2013)

Up to $75,000,000 of Shares of
Common Stock

        We have entered into a sales agreement with Cantor Fitzgerald & Co. relating to shares of our common stock offered by this prospectus supplement and the accompanying prospectus. In accordance with the terms of the sales agreement, we may offer and sell shares of our common stock having an aggregate offering price of up to $75 million from time to time through Cantor Fitzgerald & Co., acting as agent.

        Our common stock is listed on The NASDAQ Global Market under the symbol "ARRY". The last reported sale price of our common stock on The NASDAQ Global Market on March 26, 2013 was $4.93 per share.

        Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be made in sales deemed to be "at-the-market" equity offerings as defined in Rule 415 promulgated under the Securities Act of 1933, as amended, or the Securities Act, including sales made directly on or through The NASDAQ Global Market, the existing trading market for our common stock, sales made to or through a market maker other than on an exchange or otherwise, in negotiated transactions at market prices prevailing at the time of sale or at prices related to such prevailing market prices, and/or any other method permitted by law. Cantor Fitzgerald & Co. will use commercially reasonable efforts to sell on our behalf all of the shares of common stock requested to be sold by us, consistent with its normal trading and sales practices, on mutually agreed terms between Cantor Fitzgerald & Co. and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

        Cantor Fitzgerald & Co. will be entitled to compensation at a commission rate of up to 3.0% of the gross sales price per share sold, with the exact amount to be agreed to by us at the time a placement notice is delivered. In connection with its sale of common stock on our behalf, Cantor Fitzgerald & Co. may be deemed to be an "underwriter" within the meaning of the Securities Act of 1933, as amended, and the compensation of Cantor Fitzgerald & Co. may be deemed to be underwriting commissions or discounts.

        Investing in our common stock involves a high degree of risk. Before making an investment decision, please read the information contained in and incorporated by reference under the heading "Risk Factors" on page S-3 of this prospectus supplement, and under similar headings in the other documents that are filed after the date hereof and incorporated by reference into this prospectus supplement and accompanying prospectus.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement and the accompanying prospectus are truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is March 27, 2013.

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ABOUT THIS PROSPECTUS SUPPLEMENT

        This prospectus supplement and the accompanying prospectus relate to the offering of our common stock. Before buying any of the common stock that we are offering, we urge you to carefully read this prospectus supplement and the accompanying prospectus, together with the information incorporated by reference as described under the headings "Where You Can Find More Information" and "Incorporation of Certain Information by Reference" in this prospectus supplement. These documents contain important information that you should consider when making your investment decision.

        This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering of our common stock and also adds to, and updates information contained in, the accompanying prospectus and the documents incorporated by reference into this prospectus supplement and the accompanying prospectus. The second part is the accompanying prospectus, including the documents incorporated by reference into the accompanying prospectus, which provides more general information, some of which may not apply to this offering. Generally, when we refer to this prospectus, we are referring to the combined document consisting of this prospectus supplement and the accompanying prospectus.

        To the extent there is a conflict between the information contained in this prospectus supplement, on the one hand, and the information contained in the accompanying prospectus or in any document incorporated by reference into the accompanying prospectus having an earlier date than the date of this prospectus supplement, on the other hand, you should rely on the information in this prospectus supplement. In addition, if any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference into this prospectus supplement or accompanying prospectus—the statement in the document having the later date modifies or supersedes the earlier statement.

        You should rely only on the information contained in, or incorporated by reference into, this prospectus supplement, the accompanying prospectus and in any free writing prospectus that we may authorize for use in connection with this offering. We have not, and Cantor Fitzgerald has not, authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. Neither Array nor Cantor Fitzgerald is making an offer to sell or soliciting an offer to buy our securities in any jurisdiction in which an offer or solicitation is not authorized or in which the person making that offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make an offer or solicitation.

        You should assume that the information appearing in this prospectus supplement, the accompanying prospectus, the documents incorporated by reference into this prospectus supplement and the accompanying prospectus, and in any free writing prospectus that we may authorize for use in connection with this offering, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates. You should read this prospectus supplement, the accompanying prospectus, the documents incorporated by reference into this prospectus supplement and the accompanying prospectus, and any free writing prospectus that we may authorize for use in connection with this offering, in their entirety before making an investment decision. You should also read and consider the information in the documents to which we have referred you in the sections of this prospectus supplement entitled "Where You Can Find More Information" and "Incorporation of Certain Information by Reference." The information incorporated by reference is considered part of this prospectus supplement, and information we file later with the Securities and Exchange Commission may automatically update and supersede this information.

        References in this prospectus supplement to "Array," "we," "our" or "us" refer to Array BioPharma Inc., except where the context otherwise requires or as otherwise indicated.

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RISK FACTORS

        An investment in our common stock involves a high degree of risk. In addition to the other information included or incorporated by reference in this prospectus supplement and the accompanying prospectus, before making an investment decision you should carefully consider the risks described below and in the section entitled "Risk Factors" in our Annual Report on Form 10-K for our most recent fiscal year filed with the Securities and Exchange Commission, and in other reports we file with the Securities and Exchange Commission that are incorporated by reference herein. The risks and uncertainties described therein and below could adversely affect our business, operating results and financial condition, as well as cause the value of our common stock to decline. You may lose all or part of your investment as a result. You should also refer to the other information contained in this prospectus supplement and the accompanying prospectus, or incorporated by reference, including our financial statements and the notes to those statements, and the information set forth under the caption "Special Note Regarding Forward-Looking Statements." The risks described below and contained in our Annual Report on Form 10-K and in our other periodic reports are not the only ones that we face. Additional risks not presently known to us or that we currently deem immaterial may also affect our business operations, prospects and the trading price of our securities.

Risks Related to Our Stock and This Offering

Our officers and directors have significant control over us and their interests may differ from those of our stockholders.

        At December 31, 2012, our directors and officers beneficially owned or controlled approximately 5.2% of our common stock. Individually and in the aggregate, these stockholders significantly influence our management, affairs and all matters requiring stockholder approval. These stockholders may vote their shares in a way with which other stockholders do not agree. In particular, this concentration of ownership may have the effect of delaying, deferring or preventing an acquisition of us or entrenching management and may adversely affect the market price of our common stock.

Our quarterly operating results could fluctuate significantly, which could cause our stock price to decline.

        Our quarterly operating results have fluctuated in the past and are likely to fluctuate in the future. Entering into licensing or drug discovery collaborations typically involves significant technical evaluation and/or commitment of capital by our collaborators. Accordingly, negotiation can be lengthy and is subject to a number of significant risks, including collaborators' budgetary constraints and internal acceptance reviews. In addition, we have no approved drugs on the market that generate recurring royalty income, and a significant portion of our revenue is attributable to up-front and milestone payments. The achievement of milestones that trigger milestone payments occurs infrequently and the payments are non-recurring. In addition, even if a partnership yields a commercial product, the products sales on which royalties would be based may be small or insignificant. Further, some of our collaborators can influence the timing of the achievement of milestones and when we deliver products and perform services, and therefore receive revenue, under their contracts with us making it difficult to predict or control our revenue. Due to these factors, our operating results could fluctuate significantly from quarter to quarter. In addition, we may experience significant fluctuations in quarterly operating results due to factors such as general and industry-specific economic conditions that may affect the research and development expenditures of pharmaceutical and biotechnology companies.

        Due to the possibility of fluctuations in our revenue and expenses, we believe that quarter-to-quarter comparisons of our operating results are not a good indication of our future performance. Our operating results in some quarters may not meet the expectations of stock market analysts and investors. If we do not meet analysts' and/or investors' expectations, our stock price could decline.

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Because our stock price may be volatile, our stock price could experience substantial declines.

        The market price of our common stock has historically experienced and may continue to experience volatility. The high and low closing bids for our common stock were $5.96 and $3.30, respectively, for the three months ended December 31, 2012, $5.94 and $3.39, respectively, for the three months ended September 30, 2012, $3.72 and $1.77, respectively, in fiscal 2012 and $3.58 and $2.06, respectively, in fiscal 2011. Our quarterly operating results, the success or failure of our internal drug discovery efforts, developments or disputes concerning our patents or proprietary rights, changes in general conditions in the economy or the financial markets and other developments affecting our collaborators, our competitors or us could cause the market price of our common stock to fluctuate substantially. This volatility coupled with market declines in our industry over the past several years have affected the market prices of securities issued by many companies, often for reasons unrelated to their operating performance, and may adversely affect the price of our common stock. In the past, securities class action litigation has often been instituted following periods of volatility in the market price of a company's securities. A securities class action suit against us could result in potential liabilities, substantial costs and the diversion of management's attention and resources, regardless of whether we win or lose.

Because we do not intend to pay dividends, stockholders will benefit from an investment in our common stock only if it appreciates in value.

        We have never declared or paid any cash dividends on our common stock and are restricted in our ability to do so under our current credit agreement. We currently intend to retain our future earnings, if any, to finance the expansion of our business and do not expect to pay any cash dividends in the foreseeable future. As a result, the success of an investment in our common stock will depend entirely upon any future appreciation. There is no guarantee that our common stock will appreciate in value or even maintain the price at which stockholders have purchased their shares.

The ability of our stockholders to control our policies and effect a change of control of our company is limited, which may not be in the best interests of our stockholders.

        There are provisions in our certificate of incorporation and bylaws that may discourage a third party from making a proposal to acquire us, even if some of our stockholders might consider the proposal to be in their best interests. These include the following provisions in our certificate of incorporation:

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Our certificate of incorporation provides for three classes of directors with the term of office of one class expiring each year, commonly referred to as a "staggered board." By preventing stockholders from voting on the election of more than one class of directors at any annual meeting of stockholders, this provision may have the effect of keeping the current members of our board of directors in control for a longer period of time than stockholders may desire.



•

Our certificate of incorporation authorizes our board of directors to issue shares of preferred stock without stockholder approval and to establish the preferences and rights of any preferred stock issued, which would allow the board to issue one or more classes or series of preferred stock that could discourage or delay a tender offer or change in control.

        We are also subject to the business combination provisions of Section 203 of the Delaware General Corporation Law, which, in general, imposes restrictions upon acquirers of 15% or more of our stock. As a result, it is difficult for a third party to acquire control of us without the approval of the board of directors and, therefore, mergers and acquisitions of us that our stockholders may consider in their best interests may not occur.

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Future sales of our common stock may depress our stock price.

        The market price of our common stock could decline as a result of sales of substantial amounts of our common stock in the public market after the closing of this offering, or the perception that these sales could occur. In addition, these factors could make it more difficult for us to raise funds through future offerings of common stock.

        As of March 26, 2013, there were (i) 116,680,858 shares of common stock outstanding, (ii) options to purchase 8,439,822 shares of common stock outstanding under our Amended and Restated Stock Option and Incentive Plan, (iii) 25,906,983 additional shares of common stock available for future issuance under our Amended and Restated Stock Option and Incentive Plan, and (iv) 800,936 shares of common stock remaining for issuance under our Amended and Restated Employee Stock Purchase Plan. The number of shares we have reserved for issuance under our Amended and Restated Employee Stock Option and Incentive Plan may increase based on our issued and outstanding shares of common stock and we may increase the number of shares reserved for issuance under our Amended and Restated Employee Stock Purchase Plan. We may register such additional shares in the future.

        We also had outstanding as of March 26, 2013, warrants to purchase an aggregate of (i) 6,000,000 shares of our common stock at an exercise price of $3.65 per share and (ii) 6,000,000 shares of our common stock at an exercise price of $4.19 per share that were issued to Deerfield Private Design Fund, L.P., Deerfield Private Design International Fund, L.P., Deerfield Partners, L.P. and Deerfield International Limited (who we refer to collectively as the Deerfield Funds) in accordance with Facility Agreements dated April 29, 2008 and May 15, 2009 (which we refer to, as each such agreement has been amended, as the Facility Agreements). We may also be required to issue additional shares under the warrants in connection with a redemption of the warrants or upon certain failure payments that may be satisfied in shares of common stock following certain major transactions, events of default and upon the occurrence of certain events specified in the warrants. In addition, subject to certain restrictions, we may issue up to an aggregate of 11,404,000 shares of common stock under the Facility Agreements with the Deerfield Funds to satisfy payments of interest and principal thereunder.

        The shares issuable under the outstanding warrants, our Amended and Restated Stock Option and Incentive Plan and our Amended and Restated Employee Stock Purchase Plan, and to the Deerfield Funds in repayment of interest and principal under the Facility Agreements, will be available for immediate resale in the public market. The market price of our common stock could decline as a result of such resales due to the increased number of shares available for sale in the market.

We will need to raise additional capital to support our future operations, which may involve financings that could result in substantial dilution to our stockholders and the creation of additional securities senior to our common stock.

        The terms of this offering do not restrict our ability to offer additional shares of common stock or a new series of preferred stock or debt convertible into shares of our common stock or a new series of preferred stock. Our board of directors has the authority to establish the designation of shares of preferred stock that may be convertible into common stock or the issuance of debt instruments that may be convertible into common stock or preferred stock without any action by our stockholders, and to fix the rights, preferences, privileges and restrictions, including voting rights, of such shares of preferred stock or the terms of any convertible debt. Any such securities may have rights, preferences and privileges senior to those of outstanding common stock and the issuance and conversion of any such securities would further dilute the percentage ownership of our stockholders.

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We have broad discretion in the use of the net proceeds from this offering, and we may not use these proceeds effectively.

        We will retain broad discretion over the use of proceeds from this offering. We expect to use the net proceeds from this offering to fund our research and development efforts and for general corporate purposes, including working capital. We may also use the net proceeds from this offering to make payments of interest or principal under the Facility Agreements with the Deerfield Funds. A number of variables will influence our actual use of the proceeds from this offering, and our actual uses of the proceeds of this offering may vary substantially from our currently planned uses. Management could choose to spend the net proceeds from this offering in ways in which stockholders may not deem desirable, or in ways that do not improve our operating results or result in a significant return or any return at all for our stockholders. See the section entitled "Use of Proceeds" below for a more detailed discussion.

You will experience immediate dilution in the book value per share of the common stock you purchase.

        Because the price per share of our common stock being offered may be higher than the book value per share of our common stock, you may suffer immediate substantial dilution in the net tangible book value of the common stock you purchase in this offering. See the section entitled "Dilution" below for a more detailed discussion of the dilution you will incur if you purchase common stock in this offering.

A substantial number of shares of our outstanding common stock may be sold in this offering, which could cause the price of our common stock to decline.

        In this offering, we will sell up to 15,212,981 shares of common stock, or approximately 13% of our outstanding common stock as of March 26, 2013, assuming the sale of all $75 million in shares of common stock at an offering price of $4.93, the last reported sale price of our common stock on March 26, 2013. This sale and any future sales of a substantial number of shares of our common stock in the public market, or the perception that such sales may occur, could adversely affect the price of our common stock. We cannot predict the effect, if any, that market sales of those shares of common stock or the availability of those shares of common stock for sale will have on the market price of our common stock.

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

        This prospectus supplement and the accompanying prospectus contain and incorporate by reference certain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements that are not descriptions of historical facts are forward-looking statements, based on management's estimates, assumptions and projections that are subject to risks and uncertainties. These statements can generally be identified by the use of forward-looking terminology such as "believes," "expects," "intends," "may," "will," "should," or "anticipates" or similar terminology and include, but are not limited to, statements concerning our future drug development plans and projected timelines for the initiation and completion of preclinical and clinical trials by us or our collaborators; the potential for the results of ongoing preclinical or clinical trials to support regulatory approval or the marketing success of drug candidates; our plans with respect to the timing and scope of the expansion of our clinical and commercialization capabilities; other statements regarding our future product development and regulatory strategies, including with respect to specific indications; the ability of third-party contract manufacturing parties to support our drug development activities; any statements regarding our future financial performance or results of operations, our projections regarding the level of cash we expect to use in operations or the sufficiency of our capital resources to fund our operating requirements; and any other statements which are other than statements of historical fact.

        These statements reflect our current views about future events and are subject to significant risks and uncertainties, including those discussed above and those described more fully in other reports filed by Array with the Securities and Exchange Commission. Because these statements reflect our current expectations concerning future events, our actual results could differ materially from those anticipated in these forward-looking statements. The factors that could cause actual results to differ from our expectations include, but are not limited to, our ability to continue to fund and successfully progress internal research and development efforts and to create effective, commercially viable drugs; our ability to out-license our proprietary candidates on favorable terms; the ability of our collaborators and of Array to meet objectives tied to milestones and royalties; our ability to effectively and timely conduct clinical trials in light of increasing costs and difficulties in locating appropriate trial sites and in enrolling patients who meet the criteria for certain clinical trials; our ability to achieve and maintain profitability and to maintain sufficient cash resources; the extent to which the pharmaceutical and biotechnology industries are willing to in-license drug candidates for their product pipelines and to collaborate with and fund third parties on their drug discovery activities; risks associated with our dependence on our collaborators for the clinical development and commercialization of our out-licensed drug candidates; our ability to attract and retain experienced scientists, and management; and the risk factors set forth above under the caption "Risk Factors" and in other documents we file with the Securities and Exchange Commission. The forward-looking statements contained in this prospectus supplement, the accompanying prospectus or in any document incorporated by reference herein or therein represent our judgment as of the date of the respective document. Except as required by law, we undertake no duty to update any forward-looking statements to reflect the occurrence of events or circumstances that arise after the date of this prospectus supplement or the filing of the accompanying prospectus or documents incorporated by reference herein and therein that include forward-looking statements.

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USE OF PROCEEDS

        We currently intend to use the net proceeds from this offering to make payments of interest under our outstanding credit facilities with the Deerfield Funds and to fund our research and development efforts, including clinical trials for our proprietary candidates, and for general corporate purposes, including general working capital purposes. The current interest rate on our debt with the Deerfield Funds is 7.5% per annum and a payment of $20 million plus accrued interest is due on June 30, 2016 and payment of all other outstanding principal and interest is due June 30, 2015. We may also use a portion of the net proceeds to repay or refinance other existing indebtedness or other corporate borrowings, or to acquire or invest in complementary businesses, technologies, drugs, drug candidates or other intellectual property, although we have no present commitments or agreements to do so.

        The amounts and timing of these expenditures will depend on a number of factors, such as the timing and progress of our research and development efforts, technological advances and the competitive environment for our drug candidates. As of the date of this prospectus supplement, we cannot specify with certainty all of the particular uses for the net proceeds to us from this offering. Accordingly, we will retain broad discretion over the use of these proceeds. Pending these uses, we intend to invest the net proceeds in investment-grade, interest-bearing securities.

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DILUTION

        If you invest in our common stock, your interest will be diluted to the extent of the difference between the public offering price per share you pay in this offering and the net tangible book value per share of our common stock immediately after this offering. Our net tangible book value as of December 31, 2012, was approximately $(31.7) million, or $(0.27) per share of common stock. Net tangible book value per share is calculated by subtracting our total liabilities from our total tangible assets, which is total assets less intangible assets of $0, and dividing this amount by the number of shares of common stock outstanding as of December 31, 2012.

        After giving effect to the sale by us of an aggregate of $75,000,000 in shares of common stock in this offering at an assumed offering price of $4.93 per share, which was the last reported sale price of our common stock on The NASDAQ Global Market on March 26, 2013, and after deducting underwriting discounts and commissions and estimated offering expenses payable by us, our as adjusted net tangible book value as of December 31, 2012 would have been approximately $(41.7) million, or $(0.32) per share of common stock. This represents an immediate increase in the net tangible book value of $0.58 per share to our existing stockholders and an immediate dilution in the net tangible book value of $4.61 per share of common stock to new investors purchasing common stock in this offering. The following table illustrates this calculation on a per share basis:

        The information in the foregoing table does not take into account further dilution to new investors that could occur upon the exercise of outstanding options or warrants having a per share exercise price less than the per share offering price to the public in this offering. As of December 31, 2012, there were 116,660,469 shares of common stock outstanding, which does not include:

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8,653,090 shares issuable upon exercise of options outstanding as of December 31, 2012, at a weighted average exercise price of $4.78 per share;



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2,453,151 shares of common stock available for future issuance under our Amended and Restated Stock Option and Incentive Plan as of December 31, 2012;



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800,936 shares of common stock available for future issuance under our Amended and Restated Employee Stock Purchase Plan as of December 31, 2012; and



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warrants outstanding as of December 31, 2012 to purchase 6,000,000 shares at an exercise price of $3.65 per share and 6,000,000 shares at an exercise price of $4.19 per share.

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PRICE RANGE OF OUR COMMON STOCK

        Our common stock has been quoted on The NASDAQ Global Market under the symbol "ARRY" since our initial public offering on November 17, 2000. The following table sets forth, for the periods indicated, the reported high and low closing sales prices per share of our common stock as reported by The NASDAQ Global Market:

 

 

        On March 26, 2013, the closing price of our common stock as reported by The NASDAQ Global Market was $4.93 per share. As of March 25, 2013, there were approximately 59 stockholders of record of our common stock. This does not include the number of persons whose stock is held in nominee or "street name" accounts through brokers.

DIVIDEND POLICY

        We have never declared or paid any cash dividends on our common stock. We currently intend to retain any future earnings to finance the growth and development of our business. Additionally, we are currently restricted from paying any dividends under our credit facilities. Therefore, we do not anticipate that we will declare or pay any cash dividends on our common stock in the foreseeable future. Any future determination to pay cash dividends will be at the discretion of our Board of Directors and will depend on our financial condition, results of operations, capital requirements, restrictions under any existing indebtedness and other factors the Board of Directors deems relevant.

PLAN OF DISTRIBUTION

        We have entered into a Controlled Equity Offering^SM Sales Agreement, or the sales agreement, with Cantor Fitzgerald & Co., or Cantor, under which we may offer and sell up to $75,000,000 of shares from time to time through Cantor acting as agent. Cantor may sell the common stock by any method that is deemed to be an "at-the-market" equity offering as defined in Rule 415 promulgated under the Securities Act, including sales made directly on or through The NASDAQ Global Market or any other existing trading market for the common stock in the United States or to or through a market maker. With our authorization, Cantor may also sell the common stock in privately negotiated transactions.

        Each time we wish to issue and sell common stock under the sales agreement, we will notify Cantor of the number of shares to be issued, the dates on which such sales are anticipated to be made, any limitation on the number of shares to be sold in any one day and any minimum price below which

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sales may not be made. Once we have so instructed Cantor, unless Cantor declines to accept the terms of such notice, Cantor has agreed to use its commercially reasonable efforts consistent with its normal trading and sales practices to sell such shares up to the amount specified on such terms. The obligations of Cantor under the sales agreement to sell our common stock are subject to a number of conditions that we must meet.

        The settlement of sales of shares between us and Cantor is generally anticipated to occur on the third trading day following the date on which the sale was made. Sales of our common stock as contemplated in this prospectus supplement will be settled through the facilities of The Depository Trust Company or by such other means as we and Cantor may agree upon. There is no arrangement for funds to be received in an escrow, trust or similar arrangement.

        We will pay Cantor a commission equal to up to 3.0% of the aggregate gross proceeds we receive from each sale of our common stock, with the exact amount to be agreed to by us at the time a placement notice is delivered, or at such other time as we and Cantor agree. Because there is no minimum offering amount required as a condition to close this offering, the actual total public offering amount, commissions and proceeds to us, if any, are not determinable at this time. In connection with the sale of the common stock on our behalf, Cantor will be deemed to be an "underwriter" within the meaning of the Securities Act, and the compensation of Cantor will be deemed to be underwriting commissions or discounts. We have agreed to provide indemnification and contribution to Cantor with respect to certain civil liabilities, including liabilities under the Securities Act. In addition, we have agreed to reimburse Cantor for the fees and disbursements of its counsel, payable upon execution of the sales agreement, in an amount not to exceed $50,000. We estimate that the total expenses for the offering, but excluding any underwriter fees or expense reimbursement payable to Cantor under the terms of the sales agreement, will be approximately $75,000.

        The offering of our common stock pursuant to the sales agreement will terminate upon the earlier of (i) the sale of all shares of our common stock subject to the sales agreement, (ii) three years from the date of the sales agreement, or (iii) termination of the sales agreement as permitted therein. We and Cantor may each terminate the sales agreement at any time upon ten days prior notice.

        This summary of the material provisions of the sales agreement does not purport to be a complete statement of its terms and conditions. A copy of the sales agreement is filed as an exhibit to a report filed under the Exchange Act and incorporated by reference in this prospectus supplement. See "Where You Can Find More Information" and "Incorporation of Certain Information by Reference" below.

        Cantor and its affiliates may in the future provide various investment banking, commercial banking and other financial services for us and our affiliates, for which services they may in the future receive customary fees. To the extent required by Regulation M under the Exchange Act, Cantor will not engage in any market making activities involving our common stock while the offering is ongoing under this prospectus supplement.

        A prospectus supplement and the accompanying prospectus in electronic format may be made available on a website maintained by Cantor, and Cantor may distribute the prospectus supplement and the accompanying prospectus electronically.

LEGAL MATTERS

        The validity of the common stock offered by this prospectus supplement and the accompanying prospectus will be passed upon for us by Gross Hartman, LLC, Boulder, Colorado. Latham & Watkins LLP, Costa Mesa, California, is counsel for Cantor Fitzgerald & Co. in connection with this offering.

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EXPERTS

        The financial statements of Array BioPharma Inc. as of June 30, 2012 and 2011, and for each of the years in the three-year period ended June 30, 2012, and management's assessment of the effectiveness of internal control over financial reporting as of June 30, 2012 have been incorporated by reference herein and in the registration statement in reliance upon the reports of KPMG LLP, independent registered public accounting firm, incorporated by reference herein, and upon the authority of said firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

        We are subject to the informational requirements of the Exchange Act, and, in accordance therewith, we file annual, quarterly and current reports, proxy statements and other information with the Securities and Exchange Commission, or the SEC. You may read and copy any reports, statements or other information on file at the SEC's public reference room located at 100 F Street, N.E., Room 1580, Washington, D.C. 20549. Please call the SEC at 1-800-SEC-0330 for further information on the public reference room. Our SEC filings are also available on the website maintained by the SEC at http://www.sec.gov. These filings are also available to the public from commercial document retrieval services.

        We have filed with the SEC a "shelf" registration statement on Form S-3, including exhibits thereto. This prospectus supplement and accompanying prospectus, which make up part of such registration statement, do not contain all of the information in the registration statement. We have omitted parts of the registration statement from this prospectus supplement and the accompanying prospectus in accordance with the rules and regulations of the SEC. For more detail about us and any securities that may be offered by this prospectus supplement and accompanying prospectus, you may obtain a copy of the registration statement on Form S-3 and the exhibits filed with it from the address or website set forth above.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

        The SEC allows us to incorporate by reference the information that we file with the SEC, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus supplement. These documents may include periodic reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as Proxy Statements. Any documents that we subsequently file with the SEC will automatically update and replace the information previously filed with the SEC. Thus, for example, in the case of a conflict or inconsistency between information set forth in this prospectus and information incorporated by reference into this prospectus, you should rely on the information contained in the document that was filed later.

        This prospectus incorporates by reference the documents listed below that we have previously filed (under File No. 001-16633) with the SEC and any additional documents that we may file with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (which shall not include information furnished under Item 2.02 or Item 7.01 of any Current Report on Form 8-K, including any financial statements or exhibits relating thereto and furnished pursuant to Item 9.01) between the date of this prospectus and the termination of the offering of the securities. These documents contain important information about us.

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Our Annual Report on Form 10-K for the fiscal year ended June 30, 2012, filed with the SEC on August 16, 2012, including information incorporated by reference from our Definitive Proxy Statement on Schedule 14A for our annual meeting of stockholders, filed with the SEC on September 14, 2012;

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Table of Contents

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Our Quarterly Reports on Form 10-Q for the period ended September 30, 2012 filed with the SEC on October 30, 2012, and for the period ended December 31, 2012 filed with the SEC on February 6, 2013;



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Our Current Reports on Form 8-K filed with the SEC on July 19, 2012, August 1, 2012, August 31, 2012, October 29, 2012, November 5, 2012, November 6, 2012, November 7, 2012, November 8, 2012, November 9, 2012, December 4, 2012, December 10, 2012, December 31, 2012 and March 25, 2013, and the amendment to a Current Report on Form 8-K/A filed on February 1, 2013; and



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The description of our common stock contained in our Registration Statement on Form 8-A filed with the SEC on November 16, 2000, and the description of our preferred stock purchase rights contained in our Registration Statement on Form 8-A filed with the SEC on August 3, 2001, including any amendment or report filed for the purpose of updating such descriptions.

        You can obtain a copy of any or all of these documents, including any exhibits thereto, at no cost, by visiting the Investor Relations section of our web site at http://www.arraybiopharma.com or by requesting them in writing or by telephone at the following address:

Array BioPharma Inc.
3200 Walnut Street
Boulder, Colorado 80301
(303) 381-6600
Attention: Investor Relations

        Statements contained in this prospectus supplement, the accompanying prospectus and the documents incorporated by reference herein referring to the contents of any contract or other document are not necessarily complete. Where such contract or other document is listed as an exhibit to the Registration Statement on Form S-3, of which this prospectus supplement and the accompanying prospectus form a part, or any document incorporated by reference therein, each such statement is qualified by the provisions in such exhibit, to which reference is hereby made.

        Information contained on our website does not constitute a part of this prospectus supplement or the accompanying prospectus.

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PROSPECTUS

ARRAY BIOPHARMA INC.

UP TO $200,000,000 OF OUR
COMMON STOCK
PREFERRED STOCK
DEPOSITARY SHARES
DEBT SECURITIES
WARRANTS
UNITS

        We may offer from time to time up to $200,000,000 in total of any combination of the securities described in this prospectus. We may offer the common stock, preferred stock, depositary shares, debt securities and warrants (collectively, the "securities") separately or together as units, in separate series, in amounts, at prices and on terms to be set forth in one or more supplements to this prospectus. Any preferred stock we sell may be sold as either shares of preferred stock or represented by depositary shares.

        Each time we plan to issue securities, we will circulate a prospectus supplement, which will contain a description of the securities being offered and information about the specific terms, the public offering price of the securities and the net proceeds we expect to receive from such sale, and may add, update or change information contained in this prospectus. You should read this prospectus and the prospectus supplements carefully before you invest.

        The securities may be sold directly by us to investors, through agents designated from time to time or to or through underwriters or dealers. We will set forth the names of any underwriters or agents in an accompanying prospectus supplement. For additional information on the methods of sale, you should refer to the section entitled "Plan of Distribution."

        Our common stock is listed on the Nasdaq Global Market and traded under the symbol "ARRY." On December 19, 2012, the last reported sale price for our common stock was $3.59 per share.

        An investment in our securities involves a high degree of risk. You should carefully consider the "Risk Factors" contained in any supplements to this prospectus and in our most recent annual report on Form 10-K and in our other filings made with the Securities and Exchange Commission, which are incorporated by reference in this prospectus. See "Risk Factors" on page 4 of this Prospectus.

        This prospectus may not be used to offer or sell securities unless accompanied by a prospectus supplement.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is January 8, 2013

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ABOUT THIS PROSPECTUS

        This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the SEC, using a "shelf" registration process. Under this shelf process, we may from time to time offer up to $200,000,000 in any combination of the securities described in this prospectus. We may sell these securities either individually or as units consisting of one or more of such securities, each at prices and on terms to be determined at the time of sale. The common stock, preferred stock, depositary shares, debt securities and warrants are collectively referred to in this prospectus as the "securities." The securities offered pursuant to this prospectus may be one or more series of issuances, and the total offering price of the securities will not exceed $200,000,000.

        This prospectus provides you with a general description of the securities we may offer. Each time we sell securities, we will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement, or information incorporated by reference in this prospectus or any prospectus supplement that is of a more recent date, may also add, update or change information contained in this prospectus. You should read both this prospectus and any prospectus supplement together with the additional information described below under the heading "Where You Can Find More Information." These documents do not contain an offer to sell or solicitation of an offer to buy the securities in any circumstance in which the offer or solicitation is unlawful. This prospectus may not be used to consummate a sale of securities unless it is accompanied by a prospectus supplement.

        You should rely only on the information provided in the registration statement of which the prospectus is a part, this prospectus, any prospectus supplement and any documents incorporated by reference in this prospectus or any prospectus supplement. We have not authorized anyone to provide you with different information. The information in this prospectus or any prospectus supplement is accurate only as of the date of the document on the front of the document, and any information we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus or any sale of a security.

        References in this prospectus to "Array," "the company," "we," "our" or "us" refer to Array BioPharma Inc. Our trademarks include the Array BioPharma logo and the terms "ARRAY BIOPHARMA". Other trademarks and trade names appearing in this prospectus are the property of the holders of such trademarks and trade names.

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RISK FACTORS

        Investment in our securities involves risks. Prior to making a decision about investing in our securities, you should consider carefully the risk factors, together with all of the other information contained or incorporated by reference in this prospectus and any prospectus supplement, including any additional specific risks described in the section entitled "Risk Factors" contained in any supplements to this prospectus and in our most recent annual report on Form 10-K and in our quarterly reports on Form 10-Q filed with the SEC, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated herein by reference in their entirety. Each of these risk factors could adversely affect our business, operating results and financial condition, which may result in the loss of all or part of your investment.

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SPECIAL NOTE REGARDING
FORWARD-LOOKING STATEMENTS

        This prospectus contains and incorporates by reference certain forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements that are not descriptions of historical facts are forward-looking statements, based on management's estimates, assumptions and projections that are subject to risks and uncertainties. These statements can generally be identified by the use of forward-looking terminology such as "believes," "expects," "intends," "may," "will," "should," or "anticipates" or similar terminology.

        These statements involve significant risks and uncertainties, including those discussed below and those described more fully in other reports filed by Array with the SEC. Because these statements reflect our current expectations concerning future events, our actual results could differ materially from those anticipated in these forward-looking statements as a result of many factors. These factors include, but are not limited to, our ability to continue to fund and successfully progress internal research and development efforts and to create effective, commercially viable drugs; our ability to effectively and timely conduct clinical trials in light of increasing costs and difficulties in locating appropriate trial sites and in enrolling patients who meet the criteria for certain clinical trials; the extent to which the pharmaceutical and biotechnology industries are willing to in-license drug candidates for their product pipelines and to collaborate with and fund third parties on their drug discovery activities; our ability to out-license our proprietary candidates on favorable terms; risks associated with our dependence on our collaborators for the clinical development and commercialization of our out-licensed drug candidates; the ability of our collaborators and of Array to meet objectives tied to milestones and royalties; our ability to attract and retain experienced scientists and management; our ability to achieve and maintain profitability; and the risk factors set forth under the caption "Risk Factors" in our most recent annual report on Form 10-K and our quarterly reports on Form 10-Q, and any amendments thereto we file with the SEC, and in any supplements to this prospectus. The forward-looking statements contained herein represent our judgment as of the date of this prospectus. We undertake no duty or obligation to update any forward-looking statements to reflect the occurrence of events or circumstances after the date of such statements or of anticipated or unanticipated events that alter any assumptions underlying such statements.

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USE OF PROCEEDS

        Except as described in any applicable prospectus supplement we have authorized for use in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered by us hereunder, if any, to fund the costs of research and development activities and for general corporate purposes, including working capital.

        The amounts and timing of our use of the net proceeds from this offering will depend on a number of factors, such as the timing and progress of our research and development efforts, the timing and progress of any partnering and commercialization efforts and the competitive environment for our products. As of the date of this prospectus, we have no current plans, commitments or agreements with respect to any particular use of any net proceeds and we cannot specify with certainty all of the particular uses for the net proceeds to us from the sale of the securities offered by us hereunder. Accordingly, our management will have broad discretion in the timing and application of these proceeds. Pending application of the net proceeds as described above, we intend to temporarily invest the proceeds in investment-grade, interest-bearing securities.

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RATIO OF EARNINGS TO FIXED CHARGES AND PREFERENCE DIVIDENDS

        The following table sets forth our ratio of earnings to fixed charges and preference dividends to earnings for each of the periods indicated. You should read this table in conjunction with the financial statements and notes to the financial statements that are incorporated by reference in this prospectus.

        We have computed the ratio of combined fixed charges and preference dividends to earnings set forth above by dividing pre-tax loss before fixed charges and preferences by fixed charges and preference dividends. Fixed charges are the sum of the following:

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interest expensed and capitalized;



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amortized premiums, discounts and capitalized expenses related to indebtedness; and



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an estimate of the interest within rental expense.

        We did not record earnings for the three months ended September 30, 2012 or for any of the fiscal years in the five-year period ended June 30, 2012. Accordingly, our earnings were insufficient to cover fixed charges for such periods and we are unable to disclose a ratio of combined fixed charges and preference dividends to earnings for such periods. The dollar amount of the deficiency in earnings available for fixed charges and preference dividends was $11.8 million for the three months ended September 30, 2012 and $23.6 million, $56.3 million, $77.6 million, $127.8 million and $96.3 million for the years ended June 30, 2012, 2011, 2010, 2009 and 2008, respectively.

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DESCRIPTION OF CAPITAL STOCK

        The following description of our capital stock and material provisions of our amended and restated certificate of incorporation and bylaws is only a summary. The description is qualified in its entirety by the complete provisions of our amended and restated certificate of incorporation, which has been filed as an exhibit to the registration statement on Form S-1 (file no. 333-45922) filed with the SEC on September 15, 2000, and the amendments thereto filed as exhibits to the current reports on Form 8-K filed with the SEC on November 6, 2007 (File No. 001-16633) and on October 29, 2012 (File No. 001-16633), and our amended and restated bylaws, which have been filed as an exhibit to the current report on Form 8-K filed with the SEC on November 4, 2008 (File No. 001-16633). Our amended and restated certificate of incorporation authorizes the issuance of up to 220,000,000 shares of common stock, par value $0.001 per share, and 10,000,000 shares of preferred stock, par value $0.001 per share, of which our board of directors has designated 10,135 shares as Series B Convertible Preferred Stock. As of December 19, 2012, 116,135,498 shares of common stock were issued and outstanding and no shares of Series B Convertible Preferred Stock were issued and outstanding.

Listing

        Our common stock is listed on the Nasdaq Global Market and traded under the symbol "ARRY."

Transfer Agent and Registrar

        American Stock Transfer and Trust Company is our transfer agent and registrar.

Common Stock

        Each holder of common stock is entitled to one vote for each share on all matters to be voted upon by the stockholders. Holders of common stock are not entitled to cumulative voting rights with respect to the election of directors. Subject to preferences that may be applicable to any preferred stock outstanding at the time, holders of common stock are entitled to receive ratable dividends, if any, as may be declared from time to time by the board of directors out of funds legally available for that purpose. In the event of our liquidation, dissolution or winding up, holders of common stock would be entitled to share ratably in all assets remaining after the payment of liabilities and liquidation preferences on any outstanding preferred stock. Holders of common stock have no preemptive or conversion rights or other subscription rights and there are no redemption or sinking fund provisions applicable to the common stock. All outstanding shares of common stock are, and shares of common stock offered by us in this offering, when issued and paid for, will be, fully paid and nonassessable.

Preferred Stock

        Our board of directors is authorized, without stockholder approval, to issue up to an aggregate of 10,000,000 shares of preferred stock in one or more series. To date, our board of directors has designated 10,135 shares of preferred stock as Series B Convertible Preferred Stock, the rights, preferences, privileges and restrictions of which are set forth in the certificate of designation for the Series B Convertible Preferred Stock, which we filed with the SEC on May 2, 2011 as an exhibit to a current report on Form 8-K. All 10,135 shares of Series B Convertible Preferred Stock that were previously issued and were outstanding have been converted into 10,135,000 shares of common stock pursuant to the terms of the Series B Convertible Preferred Stock, and no shares of preferred stock are currently outstanding. The board of directors can fix the rights, preferences, privileges and restrictions of any other designated series preferred stock, including dividend rights, dividend rates, conversion rights, voting rights, terms of redemption, redemption prices, liquidation preferences and the number of shares constituting any series, or the designation of such series, without further vote or action by the stockholders.

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        The rights, preferences, privileges and restrictions of any series of preferred stock will be set forth in a certificate of designation relating to that series. We will incorporate by reference as an exhibit to the registration statement that includes this prospectus, the form of any certificate of designation that describes the terms of the series of preferred stock we are offering before the issuance of the related series of preferred stock. We urge you to read the complete certificate of designation containing the terms of the applicable series of preferred stock, as well as the applicable prospectus supplement related to such series. The certificate of designation will include:

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the title and stated value; the number of shares we are offering;



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the liquidation preference per share;



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the purchase price;



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the dividend rate, period and payment date and method of calculation for dividends;



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whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;



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the procedures for any auction and remarketing, if any;



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the provisions for a sinking fund, if any;



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the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;



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any listing of the preferred stock on any securities exchange or market;



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whether the preferred stock will be convertible into our common stock, and, if applicable, the conversion price, or how it will be calculated, and the conversion period;



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voting rights, if any, of the preferred stock;



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preemption rights, if any;



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restrictions on transfer, sale or other assignment, if any;



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whether interests in the preferred stock will be represented by depositary shares;



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a discussion of any material or special United States federal income tax considerations applicable to the preferred stock;



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the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;



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any limitations on issuance of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and



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any other specific terms, preferences, rights or limitations of, or restrictions on, the preferred stock.

        If we issue shares of preferred stock under this prospectus, the shares will be fully paid and non-assessable.

        The General Corporation Law of the State of Delaware, the state of our incorporation, provides that the holders of preferred stock will have the right to vote separately as a class on any proposed fundamental change in the rights of the preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

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        We may amend from time to time our amended and restated certificate of incorporation to increase the number of authorized shares of preferred stock. Any such amendment would require the approval of the holders of a majority of the voting power of the shares entitled to vote thereon.

        Future issuances of preferred stock may have the effect of delaying or preventing a change in our control or make removal of our management more difficult. Additionally, the issuance of preferred stock could decrease the amount of earnings and assets available for distribution to the holders of the common stock or could adversely affect the rights and powers, including voting rights, of the holders of our common stock. The issuance of preferred stock could also cause the market price of our common stock to decline.

Registration Rights

        Prior to our initial public offering and in connection with the sale and issuance of our Series A preferred stock in May 1998, and August 1998, our Series B preferred stock in November 1999, and our Series C preferred stock in August 2000 (all of which shares converted into shares of our common stock in connection with our initial public offering), we entered into an agreement with the investors in such financings providing for registration rights with respect to the shares of common stock, including those issuable upon conversion of each series of preferred stock, held and subsequently acquired by these investors. Currently, 2.5 million shares of our common stock are entitled to registration rights pursuant to terms and conditions of this agreement. The registration rights under this agreement allow the holders of at least 30% of the shares of common stock held by such holders then outstanding to require us to register their shares under the Securities Act of 1933, as amended, or the Securities Act, on up to two occasions, subject to limitations described in the agreement. In addition, these holders can require us to include their shares in future registrations of our shares for our account or the account of another stockholder. These holders may also require us to register their shares on up to two occasions in any calendar year on Form S-3. These registration rights are subject to limitations and conditions, including the right of underwriters to limit the number of shares of common stock held by existing stockholders to be included in a registration. The registration rights as to any holder will terminate when all securities held by the holder entitled to registration rights can be sold within a three-month period under Rule 144 of the Securities Act and when the number of shares held by the holder is less than 1% of our outstanding capital stock on an as converted to common stock basis. In addition, we are generally required to bear all expenses of registration, including the reasonable fees of a single counsel acting on behalf of all selling stockholders, except underwriting discounts and selling commissions.

        In connection with Facility Agreements we entered into with Deerfield Private Design Fund, L.P. and Deerfield Private Design International, L.P., healthcare investment funds, who we collectively refer to as the Deerfield Funds, we have issued warrants to purchase an aggregate of 12,000,000 shares of our common stock to the Deerfield Funds and entered into a Registration Rights Agreement dated May 15, 2009. Under the terms of the Registration Rights Agreement, we agreed to file a registration statement with the SEC to register the resale of the shares of the common stock subject to issuance upon the exercise of the warrants under the Securities Act of 1933. On August 31, 2009, we filed a registration statement on Form S-3 (File No. 333-161633), which we amended on Forms S-3/A filed on September 23, 2009 and on September 29, 2009, registering the shares issuable upon exercise of the warrants, and which the SEC declared effective as of October 9, 2009. We are generally required to bear all expenses of registration, including the reasonable fees of a single counsel acting on behalf of all selling stockholders, except underwriting discounts and selling commissions.

        Registration of any shares with registration rights would result in those shares becoming freely tradeable without restriction under the Securities Act. Sales of these shares, whether pursuant to Rule 144 under the Securities Act or an effective registration statement, could have a material adverse effect on the trading price of our common stock.

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Limitation of Liability of Directors and Officers

        As permitted by the Delaware General Corporation Law, our amended and restated certificate of incorporation provides that our directors are not personally liable to us or our stockholders for monetary damages for breach of fiduciary duty as a director, except for liability:

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for any breach of the director's duty of loyalty to us or our stockholders;



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for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law;



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under Section 174 of the Delaware General Corporation Law, relating to unlawful dividends or unlawful stock purchases or redemptions; or



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for any transaction from which the director derives an improper personal benefit.

        As a result of this provision, we and our stockholders may be unable to obtain monetary damages from a director for breach of his or her duty of care.

Indemnification

        Our bylaws provide for the indemnification of our directors and officers to the fullest extent authorized by the Delaware General Corporation Law. We will indemnify a director or officer in connection with an action initiated by that person if the action was authorized by our board of directors. The indemnification provided under our bylaws includes the right to be paid expenses in advance of the final disposition of a proceeding for which indemnification may be had if the director or officer agrees to repay all amounts paid in advance if it is ultimately determined that the director or officer is not entitled to be indemnified. Under our bylaws, if we do not pay a claim for indemnification within 60 days after we have received a written claim, the director or officer may bring an action to recover the unpaid amount of the claim. If successful, the director or officer also will be entitled to be paid the expense of prosecuting the action to recover these unpaid amounts.

        Our bylaws also authorize us to purchase and maintain insurance on behalf of any person who is or was one of our directors, officers, employees or agents, or is or was serving at our request as a director, officer, employee, partner or agent of another corporation or other entity or enterprise, against any liability asserted against the person or incurred by the person in any of these capacities, or arising out of the person's fulfilling one of these capacities, and related expenses. We may obtain this insurance whether or not we would have the power to indemnify the person against the claim under the provisions of the Delaware General Corporation Law. We have purchased director and officer liability insurance on behalf of our directors and officers. The indemnification provisions under our amended and restated certificate of incorporation and bylaws are not exclusive of any other rights to indemnification under any bylaw, agreement, vote of stockholders or disinterested directors or otherwise.

Anti-Takeover Provisions

General

        Our amended and restated certificate of incorporation and bylaws contain some provisions that are intended to enhance the likelihood of continuity and stability in the composition of our board of directors and in the policies formulated by our board of directors. In addition, provisions of Delaware law may hinder or delay an attempted takeover of us other than through negotiation with our board of directors. These provisions could have the effect of discouraging attempts to acquire us or remove incumbent management even if some or a majority of our stockholders believe this action is in their best interest, including attempts that might result in the stockholders receiving a premium over the market price for the shares of common stock they hold.

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Classified Board

        Our amended and restated certificate of incorporation provides for the division of our board of directors into three classes of directors serving staggered three-year terms. Our amended and restated certificate of incorporation further provides that the approval of the holders of at least two-thirds of the shares entitled to vote is necessary for the alteration, amendment or repeal of sections of our amended and restated certificate of incorporation relating to the election and classification of our board of directors, limitation of director liability, indemnification and the vote requirements for these amendments to our amended and restated certificate of incorporation. These provisions may have the effect of deterring hostile takeovers or delaying changes in control or management.

Removal of Directors and Vacancies

        Our amended and restated certificate of incorporation provides that directors may be removed only with cause upon the affirmative vote of holders representing two-thirds of our outstanding shares. In addition, vacancies and newly created directorships resulting from any increase in the size of the board of directors may be filled only by the affirmative vote of a majority of the directors then in office, even if they do not constitute a quorum, or by the sole remaining director. These provisions would prevent stockholders from removing incumbent directors without cause and filling the resulting vacancies with their own nominees.

Advance Notice Provisions for Stockholder Proposals and Stockholder Nominations of Directors

        Our bylaws establish an advance notice procedure with regard to the nomination, other than by the board of directors, of candidates for election to the board of directors and with regard to matters to be brought before an annual meeting of our stockholders by a stockholder. The stockholder's notice must contain specified information regarding the stockholder and its holdings, as well as about the director nominee and any business desired to be brought before the meeting. Although our bylaws do not give our board of directors any power to approve or disapprove stockholder nominations for the election of directors or any other business desired by stockholders to be conducted at an annual meeting, the bylaws:

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may have the effect of precluding a nomination for the election of directors or precluding the conduct of business at a particular annual meeting if the proper procedures are not followed; or



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may discourage or deter a third party from conducting a solicitation of proxies to elect its own slate of directors or otherwise attempting to obtain control of us, even if the conduct of this solicitation or the attempt to obtain control might be beneficial to us and our stockholders.

Special Stockholders' Meetings

        Under our amended and restated certificate of incorporation and bylaws, special meetings of stockholders, unless otherwise prescribed by statute, may be called only by the board of directors, the chairperson, or the chief executive officer.

Stockholder Action Without a Meeting Only by Unanimous Written Consent

        Our amended and restated certificate of incorporation provides that any action required or permitted to be taken at a stockholders' meeting may be taken without a meeting only by unanimous written consent.

Section 203 of the Delaware General Corporation Law

        Under Section 203 of the Delaware General Corporation Law, we may not engage in a "business combination," which includes a merger or sale of more than 10% of our assets, with any "interested

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stockholder," namely, a stockholder who owns 15% or more of our outstanding voting stock, as well as affiliates and associates of any of these persons, for three years following the time that stockholder became an interested stockholder, unless:

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the transaction in which the stockholder became an interested stockholder is approved by our board of directors prior to the time the interested stockholder attained that status;



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upon completion of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of our voting stock outstanding at the time the transaction commenced, excluding those shares owned by persons who are directors and also officers; or



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at or after the time the stockholder became an interested stockholder the business combination is approved by the board of directors and authorized at an annual or special meeting of stockholders by the affirmative vote of at least two-thirds of the outstanding voting stock that is not owned by the interested stockholder.

Authorized but Unissued Shares

        The authorization of undesignated preferred stock makes it possible for the board of directors to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to change control of our company. These and other provisions may have the effect of deterring hostile takeovers or delaying changes in control or management of our company.

DESCRIPTION OF DEPOSITARY SHARES

        We may offer fractional shares of preferred stock rather than full shares of preferred stock, and, in that event, will issue receipts for depositary shares. Each of these depositary shares will represent a fraction, which will be set forth in the applicable prospectus supplement, of a share of the applicable series of preferred stock.

        The shares of any series of preferred stock underlying any depositary shares that we may sell under this prospectus will be deposited under a deposit agreement between us and a depositary selected by us. Subject to the terms of the deposit agreement, each holder of a depositary share will be entitled, in proportion to the applicable fraction of a share of the preferred stock underlying the depositary share, to all of the rights, preferences and privileges, and be subject to the qualifications and restrictions, of the preferred stock underlying that depositary share.

        The depositary shares will be evidenced by depositary receipts issued under a deposit agreement. Depositary receipts will be distributed to the holders of the depositary shares that are sold in the applicable offering. We will incorporate by reference into the registration statement of which this prospectus is a part the form of any deposit agreement, including a form of depositary receipt, that describes the terms of any depositary shares we are offering before the issuance of the related depositary shares. The following summaries of material provisions of the deposit agreement, the depositary shares and the depositary receipts are subject to, and qualified in their entirety by reference to, all of the provisions of the deposit agreement applicable to a particular offering of depositary shares. We urge you to read the prospectus supplements relating to any depositary shares that are sold under this prospectus, as well as the complete deposit agreement and depositary receipt.

Form

        Pending the preparation of definitive depositary receipts, the depositary may, upon our written order, issue temporary depositary receipts substantially identical to the definitive depositary receipts but not in definitive form. These temporary depositary receipts entitle their holders to all of the rights of

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definitive depositary receipts. Temporary depositary receipts will then be exchangeable for definitive depositary receipts at our expense.

Dividends and Other Distributions

        The depositary will distribute all cash dividends or other cash distributions received with respect to the underlying preferred stock to the record holders of depositary shares in proportion to the number of depositary shares owned by those holders.

        If there is a distribution other than in cash, the depositary will distribute property received by it to the record holders of depositary shares in proportion to the number of depositary shares owned by those holders, unless the depositary determines that it is not feasible to do so. If this occurs, the depositary may, with our approval, sell the property and distribute the net proceeds from the sale to those holders in proportion to the number of depositary shares owned by them.

Withdrawal of Underlying Preferred Stock

        Except as otherwise provided in a prospectus supplement, holders may surrender depositary receipts at the principal office of the depositary and, upon payment of any unpaid amount due to the depositary, be entitled to receive the number of whole shares of underlying preferred stock and all money and other property represented by the related depositary shares. We will not issue any partial shares of preferred stock. If the holder delivers depositary receipts evidencing a number of depositary shares that represent more than a whole number of shares of preferred stock, the depositary will issue a new depositary receipt evidencing the excess number of depositary shares to the holder.

Redemption of Depositary Shares

        If the preferred stock underlying any depositary shares we may sell under this prospectus is subject to redemption, the depositary shares will be redeemed from the proceeds received by the depositary resulting from any such redemption, in whole or in part, of that underlying preferred stock. The redemption price per depositary share will be equal to the applicable fraction of the redemption price per share payable with respect to the underlying preferred stock. Whenever we redeem shares of underlying preferred stock that are held by the depositary, the depositary will redeem, as of the same redemption date, the number of depositary shares representing the shares of underlying preferred stock so redeemed. If fewer than all of the depositary shares are to be redeemed, the depositary shares to be redeemed will be selected by lot or proportionately, as may be determined by the depositary.

Voting

        Upon receipt of notice of any meeting at which holders of the preferred stock underlying any depositary shares that we may sell under this prospectus are entitled to vote, the depositary will mail the information contained in the notice to the record holders of the depositary shares. Each record holder of the depositary shares on the record date, which will be the same date as the record date for the underlying preferred stock, will be entitled to instruct the depositary as to the exercise of the voting rights pertaining to the amount of the underlying preferred stock represented by the holder's depositary shares. The depositary will then try, as far as practicable, to vote the number of shares of preferred stock underlying those depositary shares in accordance with those instructions, and we will agree to take all reasonable actions which may be deemed necessary by the depositary to enable the depositary to do so. The depositary will not vote the underlying preferred stock to the extent it does not receive specific instructions with respect to the depositary shares representing such preferred stock.

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Conversion of Preferred Stock

        If the prospectus supplement relating to any depositary shares that we may sell under this prospectus states that the underlying preferred stock is convertible into our common stock or other securities, the following will apply. The depositary shares, as such, will not be convertible into any of our securities. Rather, any holder of the depositary shares may surrender the related depositary receipts to the depositary with written instructions that direct us to cause conversion of the preferred stock represented by the depositary shares into or for whole shares of our common stock or other securities, as applicable. Upon receipt of those instructions and any amounts payable by the holder in connection with the conversion, we will cause the conversion using the same procedures as those provided for conversion of the underlying preferred stock. If only some of a holder's depositary shares are converted, a new depositary receipt or receipts will be issued to the holder for any depositary shares not converted.

Amendment and Termination of the Deposit Agreement

        The form of depositary receipt evidencing the depositary shares and any provision of the deposit agreement may at any time be amended by agreement between us and the depositary. However, any amendment which materially and adversely alters the rights of the holders of depositary shares will not be effective until 90 days after notice of that amendment has been given to the holders. Each holder of depositary shares at the time any amendment becomes effective shall be deemed to consent and agree to that amendment and to be bound by the deposit agreement as so amended. The deposit agreement may be terminated by us or by the depositary only if all outstanding depositary shares have been redeemed or converted into any other securities into which the underlying preferred stock is convertible or there has been a final distribution, including to holders of depositary receipts, of the underlying preferred stock in connection with our liquidation, dissolution or winding up.

Charges of Depositary

        We will pay all charges of the depositary, except for taxes and governmental charges and other charges as are expressly provided for in the deposit agreement to be for the account of the holders of depositary shares or persons other than ourselves who may deposit any underlying preferred stock with the depositary.

Reports

        The depositary will forward to holders of depositary receipts all notices and reports from us that we deliver to the depositary and that we are required to furnish to the holders of the underlying preferred stock.

Limitation on Liability

        Neither we nor the depositary will be liable if either of us is prevented or delayed by law or any circumstance beyond our control in performing our respective obligations under the deposit agreement. Our obligations and those of the depositary will be limited to performance of our respective duties under the deposit agreement without, in our case, negligence or bad faith or, in the case of the depositary, negligence or willful misconduct. We and the depositary may rely upon advice of counsel or accountants, or upon information provided by persons presenting the underlying preferred stock for deposit, holders of depositary receipts or other persons believed by us in good faith to be competent and on documents believed to be genuine.

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Resignation and Removal of Depositary

        The depositary may resign at any time by delivering notice to us of its election to resign. We may remove the depositary at any time. Any resignation or removal will take effect upon the appointment of a successor depositary and its acceptance of the appointment. The successor depositary must be appointed within 60 days after delivery of the notice of resignation or removal and must be a bank or trust company having its principal office in the United States and having a combined capital and surplus of at least $50,000,000.

DESCRIPTION OF DEBT SECURITIES

        We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities offered under a prospectus supplement may differ from the terms described below. Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

        We will issue the debt securities under the indenture that we will enter into with trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We have filed the form of indenture as an exhibit to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

        The following summary of material provisions of the debt securities and the indenture is subject to, and qualified in its entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

        The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.

        We may issue the debt securities issued under the indenture as "discount securities," which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with "original issue discount," or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. Material U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in any applicable prospectus supplement.

        We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

•

the title of the series of debt securities;

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•

any limit upon the aggregate principal amount that may be issued;



•

the maturity date or dates;



•

the form of the debt securities of the series;



•

the applicability of any guarantees;



•

whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;



•

whether the debt securities rank as senior debt, senior subordinated debt, subordinated debt or any combination thereof, and the terms of any subordination;



•

if the price (expressed as a percentage of the aggregate principal amount thereof) at which such debt securities will be issued is a price other than the principal amount thereof, the portion of the principal amount thereof payable upon declaration of acceleration of the maturity thereof, or if applicable, the portion of the principal amount of such debt securities that is convertible into another security or the method by which any such portion shall be determined;



•

the interest rate or rates, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;



•

our right, if any, to defer payment of interest and the maximum length of any such deferral period;



•

if applicable, the date or dates after which, or the period or periods during which, and the price or prices at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;



•

the date or dates, if any, on which, and the price or prices at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder's option to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;



•

the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;



•

any and all terms, if applicable, relating to any auction or remarketing of the debt securities of that series and any security for our obligations with respect to such debt securities and any other terms which may be advisable in connection with the marketing of debt securities of that series;



•

whether the debt securities of the series shall be issued in whole or in part in the form of a global security or securities; the terms and conditions, if any, upon which such global security or securities may be exchanged in whole or in part for other individual securities; and the depositary for such global security or securities;



•

if applicable, the provisions relating to conversion or exchange of any debt securities of the series and the terms and conditions upon which such debt securities will be so convertible or exchangeable, including the conversion or exchange price, as applicable, or how it will be calculated and may be adjusted, any mandatory or optional (at our option or the holders' option) conversion or exchange features, the applicable conversion or exchange period and the manner of settlement for any conversion or exchange;



•

if other than the full principal amount thereof, the portion of the principal amount of debt securities of the series which shall be payable upon declaration of acceleration of the maturity thereof;

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•

additions to or changes in the covenants applicable to the particular debt securities being issued, including, among others, the consolidation, merger or sale covenant;



•

additions to or changes in the events of default with respect to the securities and any change in the right of the trustee or the holders to declare the principal, premium, if any, and interest, if any, with respect to such securities to be due and payable;



•

additions to or changes in or deletions of the provisions relating to covenant defeasance and legal defeasance;



•

additions to or changes in the provisions relating to satisfaction and discharge of the indenture;



•

additions to or changes in the provisions relating to the modification of the indenture both with and without the consent of holders of debt securities issued under the indenture;



•

the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars;



•

whether interest will be payable in cash or additional debt securities at our or the holders' option and the terms and conditions upon which the election may be made;



•

the terms and conditions, if any, upon which we will pay amounts in addition to the stated interest, premium, if any and principal amounts of the debt securities of the series to any holder that is not a "United States person" for federal tax purposes;



•

any restrictions on transfer, sale or assignment of the debt securities of the series; and



•

any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, any other additions or changes in the provisions of the indenture, and any terms that may be required by us or advisable under applicable laws or regulations.

Conversion or Exchange Rights

        We will set forth in the prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities or other property or assets. We will include provisions as to settlement upon conversion or exchange and whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities or units of other property or assets that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

        Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of all or substantially all of our assets. However, any successor to or acquirer of such assets must assume all of our obligations under the indenture or the debt securities, as appropriate. If the debt securities are convertible for our other securities, the person with whom we consolidate or merge or to whom we sell all of our property must make provisions for the conversion of the debt securities into securities that the holders of the debt securities would have received if they had converted the debt securities before the consolidation, merger or sale.

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Events of Default Under the Indenture

        Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that we may issue:

•

if we fail to pay any installment of interest on any series of debt securities, as and when due and payable, and such default continues for a period of 90 days;



•

if we fail to pay the principal of, or premium, if any, on any series of debt securities as and when due and payable whether at maturity, upon redemption, by declaration or otherwise, or in any payment required by any sinking or analogous fund established with respect to such series;



•

if we fail to observe or perform any other covenant or agreement contained in the debt securities or the indenture, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive written notice of such failure, from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and



•

if specified events of bankruptcy, insolvency or reorganization occur.

        If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal of, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

        The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

        Subject to the terms of the indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

•

the direction so given by the holder is not in conflict with any law or the applicable indenture; and



•

subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

        A holder of the debt securities of any series will have the right to institute a proceeding under the indenture or to appoint a receiver or trustee, or to seek other remedies only if:

•

the holder has given written notice to the trustee of a continuing event of default with respect to that series;

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•

the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request, and such holders have offered reasonable indemnity to the trustee to institute the proceeding as trustee; and



•

the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

        These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

        We will periodically file statements with the trustee regarding our compliance with specified covenants in the indenture.

Modification of Indenture; Waiver

        We and the trustee may change an indenture without the consent of any holders with respect to specific matters:

•

to cure any ambiguity, defect or inconsistency in the indenture or in the debt securities of any series;



•

to comply with the provisions described above under "Description of Debt Securities—Consolidation, Merger or Sale;"



•

to provide for uncertificated debt securities in addition to or in place of certificated debt securities and to make all appropriate changes for such purpose;



•

to add to our covenants, restrictions, conditions or provisions such new covenants, restrictions, conditions or provisions for the benefit of the holders of all or any series of debt securities, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred upon us in the indenture;



•

to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;



•

to make any change that does not adversely affect the interests of any holder of debt securities of any series in any material respect;



•

to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided above under "Description of Debt Securities—General" to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;



•

to evidence and provide for the acceptance of appointment under any indenture by a successor trustee; or



•

to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act.

        In addition, under the indenture, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we

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and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

•

extending the fixed maturity of any debt securities of any series;



•

reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption of any series of any debt securities; or



•

reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Discharge

        Each indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

•

provide for payment;



•

register the transfer or exchange of debt securities of the series;



•

replace stolen, lost or mutilated debt securities of the series;



•

pay principal of and premium and interest on any debt securities of the series;



•

maintain paying agencies;



•

hold monies for payment in trust;



•

recover excess money held by the trustee;



•

compensate and indemnify the trustee; and



•

appoint any successor trustee.

        In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

        We will issue the debt securities of each series only in fully registered form without coupons and, unless we provide otherwise in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indenture provides that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company, or DTC, or another depositary named by us and identified in a prospectus supplement with respect to that series. To the extent the debt securities of a series are issued in global form and as book-entry, a description of terms relating will be set forth in the applicable prospectus supplement.

        At the option of the holder, subject to the terms of the indenture and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

        Subject to the terms of the indenture and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the

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debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

        We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

        If we elect to redeem the debt securities of any series, we will not be required to:

•

issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or



•

register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

Information Concerning the Trustee

        The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indenture at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

        Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

        We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

        All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

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Governing Law

        The indenture and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act of 1939 is applicable.

Subordination of Subordinated Debt Securities

        The subordinated debt securities will be subordinate and junior in priority of payment to certain of our other indebtedness to the extent described in a prospectus supplement. The indenture in the form initially filed as exhibits to the registration statement of which this prospectus is a part do not limit the amount of indebtedness which we may incur, including senior indebtedness or subordinated indebtedness, and do not limit us from issuing any other debt, including secured debt or unsecured debt

DESCRIPTION OF WARRANTS

General

        The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the warrants that we may offer under this prospectus and the related warrant agreements and warrant certificates. While the terms summarized below will apply generally to any warrants we may offer, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. The form for each type of warrant will be filed as an exhibit to the registration statement of which this prospectus is a part.

        We may issue, together with other securities or separately, warrants to purchase preferred stock or common stock. We will issue the warrants under warrant agreements to be entered into between us and a bank or trust company, as warrant agent, all as shall be set forth in the applicable prospectus supplement. The warrant agent will act solely as our agent in connection with the warrants of the series being offered and will not assume any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants.

        Further terms of the warrants will be set forth in the applicable prospectus supplement, including, where applicable, the following:

•

the title of such warrants;



•

the aggregate number of warrants;



•

the price or prices at which the warrants will be issued;



•

the designation, terms and number of shares of common stock, preferred stock or depositary shares purchasable upon exercise of the warrants;



•

the designation and terms of the securities with which the warrants are issued and the number of warrants issued with such securities;



•

the date on and after which the warrants and the related securities will be separately transferable, including any limitations on ownership and transfer of the warrants;



•

in the case of warrants to purchase common stock, preferred stock or depositary shares, the price at which each share of common stock, preferred stock or depositary share purchasable upon exercise of the warrants may be purchased;



•

any provisions for adjustment of the number or amount of securities receivable upon exercise of the warrants;

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•

the dates on which the right to exercise the warrants shall commence and expire;



•

the minimum or maximum amount of warrants that may be exercised at any one time;



•

information with respect to book-entry procedures, if any;



•

a discussion of certain federal income tax consequences; and



•

any other terms of the warrants, including terms, procedures and limitations relating to the exchange and exercise of the warrants.

        Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including in the case of warrants to purchase common stock, preferred stock or depositary shares, the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding up or to exercise voting rights, if any.

Exercise of Warrants

        Each warrant will entitle the holder thereof to purchase for cash the securities at the exercise price as shall in each case be set forth in, or be determinable as set forth in, the applicable prospectus supplement. Warrants may be exercised at any time up to the close of business on the expiration date set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

        Holders of the warrants may exercise the warrants by delivering the warrant certificate representing the warrants to be exercised together with specified information, and paying the required amount to the warrant agent in immediately available funds, as provided in the applicable prospectus supplement. We will set forth on the reverse side of the warrant certificate and in the applicable prospectus supplement the information that the holder of the warrant will be required to deliver to the warrant agent.

        Warrants may be exercised as set forth in the applicable prospectus supplement relating to the warrants offered thereby. Upon receipt of payment of the exercise price and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement, we will, as soon as practicable, forward the purchased securities. If less than all of the warrants represented by the warrant certificate are exercised, a new warrant certificate will be issued for the remaining warrants. If we so indicate in the applicable prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

Enforceability of Rights of Holders of Warrants

        Each warrant agent will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as a warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, that holder's warrants.

Outstanding Warrants

        As of December 19, 2012, there were outstanding warrants to purchase 6,000,000 shares of our common stock at an exercise price of $3.65 per share and warrants to purchase 6,000,000 shares of our common stock at an exercise price of $4.19 per share. The warrants were amended in May 2011 to

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extend the April 29, 2014 expiration date to June 30, 2016. The warrants are not exercisable to the extent such exercise would cause the holder thereof to beneficially own more than 9.98% of our outstanding capital stock. Such warrants were filed as an exhibit to an amendment to a current report on Form 8-K/A we filed with the SEC on September 23, 2009 (File No. 001-16633), and the amendment to the warrants extending the term of the warrants was filed as an exhibit to our current report on Form 8-K as of May 2, 2011 (File No. 001-16633).

DESCRIPTION OF UNITS

        The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the units that we may offer under this prospectus. While the terms we have summarized below will apply generally to any units that we may offer under this prospectus, we will describe the particular terms of any series of units in more detail in the applicable prospectus supplement. The terms of any units offered under a prospectus supplement may differ from the terms described below. However, no prospectus supplement will fundamentally change the terms that are set forth in this prospectus or offer a security that is not registered and described in this prospectus at the time of its effectiveness.

        We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from a current report on Form 8-K that we file with the SEC, the form of unit agreement that describes the terms of the series of units we are offering, and any supplemental agreements, before the issuance of the related series of units. The following summaries of material terms and provisions of the units are subject to, and qualified in their entirety by reference to, all the provisions of the unit agreement and any supplemental agreements applicable to a particular series of units. We urge you to read the applicable prospectus supplements related to the particular series of units that we sell under this prospectus, as well as the complete unit agreement and any supplemental agreements that contain the terms of the units.

General

        We may issue units comprised of one or more debt securities, shares of common stock, shares of preferred stock and warrants in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date.

        We will describe in the applicable prospectus supplement the terms of the series of units, including:

•

the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;



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any provisions of the governing unit agreement that differ from those described below; and



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any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units.

        The provisions described in this section, as well as those described under "Description of Capital Stock," "Description of Depositary Shares," "Description of Debt Securities" and "Description of Warrants" will apply to each unit and to any common stock, preferred stock, debt security or warrant included in each unit, respectively.

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Issuance in Series

        We may issue units in such amounts and in numerous distinct series as we determine.

Enforceability of Rights by Holders of Units

        Each unit agent will act solely as our agent under the applicable unit agreement and will not assume any obligation or relationship of agency or trust with any holder of any unit. A single bank or trust company may act as unit agent for more than one series of units. A unit agent will have no duty or responsibility in case of any default by us under the applicable unit agreement or unit, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a unit may, without the consent of the related unit agent or the holder of any other unit, enforce by appropriate legal action its rights as holder under any security included in the unit.

Title

        We, the unit agents and any of their agents may treat the registered holder of any unit certificate as an absolute owner of the units evidenced by that certificate for any purpose and as the person entitled to exercise the rights attaching to the units so requested, despite any notice to the contrary. See "Legal Ownership of Securities."

LEGAL OWNERSHIP OF SECURITIES

        We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the "holders" of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as "indirect holders" of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

        We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary's book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

        Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

        As a result, investors in a book-entry security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary's book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not holders, of the securities.

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Street Name Holders

        We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in "street name." Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

        For securities held in street name, we will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

        Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

        For example, once we make a payment or give a notice to the holder, we have no further responsibility for the payment or notice even if that holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may want to obtain the approval of the holders to amend an indenture, to relieve us of the consequences of a default or of our obligation to comply with a particular provision of the indenture or for other purposes. In such an event, we would seek approval only from the holders, and not the indirect holders, of the securities. Whether and how the holders contact the indirect holders is up to the holders.

Special Considerations For Indirect Holders

        If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

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how it handles securities payments and notices;



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whether it imposes fees or charges;



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how it would handle a request for the holders' consent, if ever required;



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whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if that is permitted in the future;



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how it would exercise rights under the securities if there were a default or other event triggering the need for holders to act to protect their interests; and



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if the securities are in book-entry form, how the depositary's rules and procedures will affect these matters.

Global Securities

        A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

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        Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, DTC will be the depositary for all securities issued in book-entry form.

        A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under "Special Situations When a Global Security Will Be Terminated." As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a holder of the security, but only an indirect holder of a beneficial interest in the global security.

        If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations For Global Securities

        As an indirect holder, an investor's rights relating to a global security will be governed by the account rules of the investor's financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

        If securities are issued only in the form of a global security, an investor should be aware of the following:

•

An investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;



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An investor will be an indirect holder and must look to his or her own bank or broker for payments on the securities and protection of his or her legal rights relating to the securities, as we describe above;



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An investor may not be able to sell interests in the securities to some insurance companies and to other institutions that are required by law to own their securities in non-book-entry form;



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An investor may not be able to pledge his or her interest in a global security in circumstances where certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;



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The depositary's policies, which may change from time to time, will govern payments, transfers, exchanges and other matters relating to an investor's interest in a global security;



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We and any applicable trustee have no responsibility for any aspect of the depositary's actions or for its records of ownership interests in a global security, nor do we or the trustee supervise the depositary in any way;

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•

The depositary may, and we understand that DTC will, require that those who purchase and sell interests in a global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and



•

Financial institutions that participate in the depositary's book-entry system, and through which an investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities.

        There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When A Global Security Will Be Terminated

        In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

        The global security will terminate when the following special situations occur:

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if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for that global security and we do not appoint another institution to act as depositary within 90 days;



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if we notify any applicable trustee that we wish to terminate that global security; or



•

if an event of default has occurred with regard to securities represented by that global security and has not been cured or waived.

        The prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

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PLAN OF DISTRIBUTION

        We may sell the securities being offered by this prospectus separately or together through any of the following methods:

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directly to purchasers;



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through agents;



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to or through one or more underwriters or dealers;



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through a block trade in which the broker or dealer engaged to handle the block trade will attempt to sell the securities as agent, but may position and resell a portion of the block as principal to facilitate the transaction; and



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through a combination of any of these methods of sale.

        We may effect the distribution of the securities from time to time in one or more transactions:

•

at a fixed price or prices, which may be changed from time to time;



•

at market prices prevailing at the times of sale;



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at prices related to such prevailing market prices; or



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at negotiated prices.

        Each time we offer a type or series of securities, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, as described above under "SUMMARY—Securities Registered Hereby that We May Offer", including, to the extent applicable:

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the name or names of the underwriters, if any;



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the purchase price of the securities or other consideration therefor, and the proceeds, if any, we will receive from the sale;



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any over-allotment options under which underwriters may purchase additional securities from us;



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any agency fees or underwriting discounts and other items constituting agents' or underwriters' compensation;



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any public offering price;



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any discounts or concessions allowed or reallowed or paid to dealers; and



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any securities exchange or market on which the securities may be listed.

        Only underwriters named in the prospectus supplement will be underwriters of the securities offered by the prospectus supplement.

        Agents.    We may solicit offers to purchase the securities offered by this prospectus through agents we designate from time to time. We will name any agent involved in the offer or sale of the securities and set forth any commissions payable by us to an agent in the applicable prospectus supplement. Unless otherwise indicated in the prospectus supplement, any agent will be acting on a best efforts basis for the period of his or her appointment. Any agent may be deemed to be an "underwriter" of the securities as that term is defined in the Securities Act of 1933, or the Securities Act.

        Underwriters.    If we use an underwriter or underwriters in the sale of securities, we will execute an underwriting agreement with the underwriter or underwriters at the time we reach an agreement for sale. The underwriter or underwriters will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at

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varying prices determined at the time of sale. The obligations of an underwriter or underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement. We will set forth in the prospectus supplement the names of the specific managing underwriter or underwriters, as well as any other underwriters, and the terms of the transactions, including compensation of the underwriters and dealers. This compensation may be in the form of discounts, concessions or commissions. We may use underwriters with whom we have a material relationship. Underwriters and others participating in any offering of the securities may engage in transactions that stabilize, maintain or otherwise affect the price of the securities. We will describe any such relationship and any of these activities in the prospectus supplement.

        Dealers.    If a dealer is used in the sale of the securities, an underwriter or we will sell securities to the dealer, as principal. The dealer may then resell the securities to the public at varying prices to be determined by the dealer at the time of resale. The prospectus supplement will set forth the name of the dealer and the terms of the transactions.

        Direct Sales.    We may directly solicit offers to purchase the securities, and we may sell directly to institutional investors or others. These persons may be deemed to be underwriters within the meaning of the Securities Act with respect to any resale of the securities. The prospectus supplement will describe the terms of any direct sales, including the terms of any bidding or auction process.

        Indemnification.    Agreements we enter into with agents, underwriters and dealers may entitle them to indemnification by us against specified liabilities, including liabilities under the Securities Act, or to contribution by us to payments they may be required to make in respect of these liabilities. The prospectus supplement will describe the terms and conditions of indemnification or contribution.

        Delayed Delivery Contracts.    We may authorize underwriters, dealers and agents to solicit offers by certain institutional investors to purchase offered securities under contracts providing for payment and delivery on a future date specified in the prospectus supplement. The prospectus supplement will also describe the public offering price for the securities and the commission payable for solicitation of these delayed delivery contracts. Delayed delivery contracts will contain definite fixed price and quantity terms. The obligations of a purchaser under these delayed delivery contracts will be subject to only two conditions:

•

that the institution's purchase of the securities at the time of delivery of the securities is not prohibited under the law of any jurisdiction to which the institution is subject; and



•

that we shall have sold to the underwriters the total principal amount of the offered securities, less the principal amount covered by the delayed delivery contracts.

        Stabilization Activities.    To the extent permitted by and in accordance with Regulation M under the Securities Exchange Act of 1934, as amended, or the Exchange Act, in connection with an offering an underwriter may engage in over-allotments, stabilizing transactions, short covering transactions and penalty bids. Over-allotments involve sales in excess of the offering size, which creates a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would be otherwise. If commenced, the underwriters may discontinue any of these activities at any time.

        Passive Market Making.    To the extent permitted by and in accordance with Regulation M under the Exchange Act, any underwriters who are qualified market makers on the Nasdaq Global Market may engage in passive market making transactions in the securities on the Nasdaq Global Market

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during the business day prior to the pricing of an offering, before the commencement of offers or sales of the securities. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker's bid, however, the passive market maker's bid must then be lowered when certain purchase limits are exceeded.

        Trading Markets and Listing.    Unless otherwise specified in the applicable prospectus supplement, each class or series of securities will be a new issue with no established trading market, other than our common stock, which is listed on the Nasdaq Global Market. We may elect to list any other class or series of securities on any exchange, but we are not obligated to do so. It is possible that one or more underwriters may make a market in a class or series of securities, but the underwriters will not be obligated to do so and may discontinue any market making at any time. We cannot give any assurance as to the liquidity of the trading market for any of the securities we may offer under this prospectus.

        In compliance with guidelines of the Financial Industry Regulatory Authority, or FINRA, the maximum consideration or discount to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amount of the securities offered pursuant to this prospectus and any applicable prospectus supplement.

        No securities may be sold under this prospectus without delivery, in paper format, in electronic format on the Internet, or both, of the applicable prospectus supplement describing the method and terms of the offering.

LEGAL MATTERS

        Gross Hartman LLC, Boulder, Colorado, will provide us with an opinion as to certain legal matters in connection with the issuance and sale of the securities. Clateman + Associates, LLC, Boulder, Colorado, will provide us with an opinion as to certain legal matters in connection with the issuance and sale of the debt securities.

EXPERTS

        The financial statements of Array BioPharma Inc. as of June 30, 2012 and 2011, and for each of the years in the three-year period ended June 30, 2012, and management's assessment of the effectiveness of internal control over financial reporting as of June 30, 2012 have been incorporated by reference herein and in the registration statement in reliance upon the reports of KPMG LLP, independent registered public accounting firm, incorporated by reference herein and upon the authority of said firm as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

        We have filed with the SEC a registration statement under the Securities Act that registers the distribution of the securities offered under this prospectus. The registration statement, including the attached exhibits and schedules and the information incorporated by reference, contains important information about our company and the securities. The rules and regulations of the SEC allow us to omit from this prospectus certain information included in the registration statement. In addition, we file annual, quarterly and special reports, proxy statements and other information with the SEC. You may read and copy this information and the registration statement at the SEC's Public Reference Room located at 100 F Street, N.E., Washington D.C. 20549. Please call the SEC at 1-800-SEC-0330 for more information about the operation of the public reference room.

        In addition, any information we file with the SEC, including the registration statement and the documents incorporated by reference into this prospectus, and the exhibits thereto, is also available on

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the SEC's website at http://www.sec.gov. We also maintain a web site at http://www.arraybiopharma.com, which provides additional information about our company and through which you can also access our SEC filings. The information set forth on our web site is not part of this prospectus.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

        The SEC allows us to incorporate by reference the information that we file with the SEC, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. These documents may include periodic reports, such as Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, as well as Proxy Statements. Any documents that we subsequently file with the SEC will automatically update and replace the information previously filed with the SEC. Thus, for example, in the case of a conflict or inconsistency between information set forth in this prospectus and information incorporated by reference into this prospectus, you should rely on the information contained in the document that was filed later.

        This prospectus incorporates by reference the documents listed below that we have previously filed with the SEC (under File No. 001-16633) and any additional documents that we may file with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act between the date of this prospectus and the termination of the offering of the securities. These documents contain important information about us.

•

our Annual Report on Form 10-K for the fiscal year ended June 30, 2012 filed with the Securities and Exchange Commission on August 16, 2012;



•

the information specifically incorporated by reference into our Annual Report on Form 10-K for the fiscal year ended June 30, 2012 from our definitive proxy statement on Schedule 14A, filed with the Securities and Exchange Commission on September 14, 2012;



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our Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2012 and filed with the Commission on October 30, 2012;



•

our Current Reports on Form 8-K, filed with the Securities and Exchange Commission on July 19, 2012, August 1, 2012, August 31, 2012, October 29, 2012, November 5, 2012, November 6, 2012, November 7, 2012, November 8, 2012, November 9, 2012, December 4, 2012 and December 10, 2012; and



•

the description of our common stock contained in our registration statement on Form 8-A filed with the Securities and Exchange Commission on November 16, 2000, including any amendments or reports filed for the purpose of updating such description.

        You can obtain a copy of any or all of these documents, including any exhibits thereto, at no cost, by visiting the Investor Relations section of our web site at http://www.arraybiopharma.com or by requesting them in writing or by telephone at the following address:

Array BioPharma Inc.
3200 Walnut Street
Boulder, Colorado 80301
(303) 381-6600
Attention: Investor Relations

        See also the section entitled "Where You Can Find More Information" below.

        Statements contained in this prospectus and the documents incorporated by reference herein referring to the contents of any contract or other document are not necessarily complete. Where such

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contract or other document is listed as an exhibit to the Registration Statement on Form S-3, of which this prospectus forms a part, or any document incorporated by reference therein, each such statement is qualified by the provisions in such exhibit, to which reference is hereby made.

        Information contained on our website does not constitute a part of this prospectus.

DISCLOSURE OF COMMISSION POSITION ON INDEMNIFICATION FOR
SECURITIES ACT LIABILITIES

        Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange Commission such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

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Common Stock

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Prospectus Supplement

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March 27, 2013

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