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                                                                     EXHIBIT 4.2

                            OSI PHARMACEUTICALS, INC.
                        1999 INCENTIVE AND NON-QUALIFIED
                                STOCK OPTION PLAN

1.       Purpose

                  The purpose of this 1999 Incentive and Non-Qualified Stock
         Option Plan (the "Plan") is to encourage and enable selected
         management, other employees, directors (whether or not employees), and
         consultants of OSI Pharmaceuticals, Inc. (the "Company") or a parent or
         subsidiary of the Company to acquire a proprietary interest in the
         Company through the ownership of common stock, par value $.01 per share
         (the "Common Stock"), of the Company. Such ownership will provide such
         employees, directors, and consultants with a more direct stake in the
         future welfare of the Company, and encourage them to remain with the
         Company or a parent or subsidiary of the Company. It is also expected
         that the Plan will encourage qualified persons to seek and accept
         employment with, or become associated with, the Company or a parent or
         subsidiary of the Company. Pursuant to the Plan, the Company may grant
         (i) "incentive stock options," within the meaning of Section 422 of the
         Internal Revenue Code of 1986, as amended (the "Code") and (ii) stock
         options that do not qualify as incentive stock options ("non-qualified
         stock options"). No option granted under the Plan shall be treated as
         an incentive stock option unless the stock option agreement which
         evidences the grant refers to such option as an incentive stock option
         and such option satisfies the requirements of Section 422 of the Code.

                  As used herein, the term "parent" or "subsidiary" shall mean
         any present or future corporation which is or would be a "parent
         corporation" or "subsidiary corporation" of the Company as the term is
         defined in Section 424 of the Code (determined as if the Company were
         the employer corporation).

2.       Administration of the Plan

                  The Plan shall be administered by a committee (the
         "Committee") as appointed from time to time by the Board of Directors
         of the Company, which may be the Compensation Committee of the Board of
         Directors. Except as otherwise specifically provided herein, no person,
         other than members of the Committee, shall have any discretion as to
         decisions regarding the Plan. The Company may engage a third party to
         administer routine matters under the Plan, such as establishing and
         maintaining accounts for Plan participants and facilitating
         transactions by participants pursuant to the Plan.

                  In administering the Plan, the Committee may adopt rules and
         regulations for carrying out the Plan. The interpretations and
         decisions made by the Committee with regard to any question arising
         under the Plan shall be final and conclusive on all persons
         participating or eligible to participate in the Plan. Subject to the
         provisions of the Plan, the Committee shall determine the terms of all
         options granted pursuant to the Plan, including, but not limited to,
         the persons to whom, and the time or times at which, grants shall be
         made, the number of shares to be covered by each option, the duration
         of options, the exercisability of options, whether options shall be
         treated as incentive stock options, and the option price.

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3.       Shares of Stock Subject to the Plan

                  Except as provided in paragraphs 6(h), 6(i) and 7 hereof, the
         number of shares that may be issued or transferred pursuant to the
         exercise of options granted under the Plan shall not exceed 2,000,000
         shares of Common Stock. Such shares may be authorized and unissued
         shares or previously issued shares acquired or to be acquired by the
         Company and held in treasury. Any shares subject to an option which for
         any reason expires or is terminated unexercised as to such shares may
         again be subject to an option right under the Plan. The aggregate Fair
         Market Value, as defined in paragraph 6(k) below (determined at the
         time the option is granted), of the shares with respect to which
         incentive stock options are exercisable for the first time by an
         optionee during any calendar year (under the Plan and all plans of the
         Company and any parent or subsidiary of the Company) shall not exceed
         $100,000.

4.       Eligibility

                  Incentive stock options may be granted only to management and
         other employees who are employed by the Company or a parent or
         subsidiary of the Company. Incentive stock options may be granted to a
         director of the Company or a parent or subsidiary of the Company,
         provided that the director is also an officer or employee.
         Non-qualified stock options may be granted to directors, officers,
         employees and consultants of the Company.

5.       Granting of options

                  No options pursuant to this Plan may be granted after the
         close of business on June 22, 2009. The date of the grant of any option
         shall be the date on which the Committee authorizes the grant of such
         option.

6.       Options

                  Options shall be evidenced by stock option agreements in such
         form, consistent with the Plan, as the Committee shall approve from
         time to time, which agreements need not be identical and shall be
         subject to the following terms and conditions:

                           (a)      Option Price. The purchase price under each
                  incentive stock option shall be not less than 100% of the Fair
                  Market Value of the Common Stock at the time the option is
                  granted and not less than the par value of the Common Stock.
                  In the case of an incentive stock option granted to an
                  employee owning, actually or constructively under Section
                  424(d) of the Code, more than 10% of the total combined voting
                  power of all classes of stock of the Company or of any parent
                  or subsidiary of the Company (a "10% Stockholder") the option
                  price shall not be less than 110% of the Fair Market Value of
                  the Common Stock at the time of the grant. The purchase price
                  under each non-qualified stock option shall be specified by
                  the Committee, but shall in no case be less than the greater
                  of 50% of the Fair Market Value of the Common Stock at the
                  time the option is granted and the par value of such Common
                  Stock.

                           (b)      Medium and Time of Payment. Stock purchased
                  pursuant to the exercise of an option shall at the time of
                  purchase be paid for in full in cash, or, upon conditions
                  established by the Committee, by delivery of shares of Common
                  Stock owned by the recipient. If payment is made by the
                  delivery of shares, the value of the

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                  shares delivered shall be the Fair Market Value of such shares
                  on the date of exercise of the option. In addition, unless
                  otherwise provided by the Committee an "in the money"
                  non-qualified stock option may be exercised on a "cashless"
                  basis in exchange for the issuance to the optionee (or other
                  person entitled to exercise the option) of the largest whole
                  number of shares having an aggregate value equal to the value
                  of such option on the date of exercise. For this purpose, the
                  value of the shares delivered by the Company and the value of
                  the option being exercised shall be determined based on the
                  Fair Market Value of the Common Stock on the date of exercise
                  of the option. Upon receipt of payment and such documentation
                  as the Company may deem necessary to establish compliance with
                  the Securities Act of 1933, as amended (the "Securities Act"),
                  the Company shall, without stock transfer tax to the optionee
                  or other person entitled to exercise the option, deliver to
                  the person exercising the option a certificate or certificates
                  for such shares. It shall be a condition to the performance of
                  the Company's obligation to issue or transfer Common Stock
                  upon exercise of an option or options that the optionee pay,
                  or make provision satisfactory to the Company for the payment
                  of, any taxes (other than stock transfer taxes) the Company is
                  obligated to collect with respect to the issue or transfer of
                  Common Stock upon such exercise, including any federal, state,
                  or local withholding taxes.

                           (c)      Waiting Period. The waiting period and time
                  for exercising an option shall be prescribed by the Committee
                  in each particular case; provided, however, that no option may
                  be exercised after 10 years from the date it is granted. In
                  the case of an incentive stock option granted to a 10%
                  Stockholder, such option, by its terms, shall be exercisable
                  only within five years from the date of grant.

                           (d)      Rights as a Stockholder. A recipient of
                  options shall have no rights as a stockholder with respect to
                  any shares issuable or transferable upon exercise thereof
                  until the date a stock certificate is issued to him for such
                  shares. Except as otherwise expressly provided in the Plan, no
                  adjustment shall be made for dividends or other rights for
                  which the record date is prior to the date such stock
                  certificate is issued.

                           (e)      Non-Assignability of Options. No incentive
                  stock option and, except as may otherwise be specifically
                  provided by the Committee, no non-qualified stock options,
                  shall be assignable or transferable by the recipient except by
                  will or by the laws of descent and distribution. During the
                  lifetime of a recipient, incentive stock options and, except
                  as may otherwise be specifically provided by the Committee,
                  non-qualified stock options, shall be exercisable only by such
                  recipient. If the Committee approves provisions in any
                  particular case allowing for assignment or transfer of a
                  non-qualified stock option, then such option will nonetheless
                  be subject to a six-month holding period commencing on the
                  date of grant during which period the recipient will not be
                  permitted to assign or transfer such option, unless the
                  Committee further specifically provides for the assignability
                  or transferability of such option during this period. See
                  paragraph 8 hereof for restrictions on sale of shares.

                           (f)      Effect of Termination of Employment. If a
                  recipient's employment (or service as an officer, director or
                  consultant) shall terminate for any reason, other than death
                  or Retirement (as defined below), the right of the recipient
                  to exercise any option otherwise exercisable on the date of
                  such termination shall expire unless such right is exercised
                  within a period of 90 days after the date of such termination.
                  The term

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                  "Retirement" shall mean the voluntary termination of
                  employment (or service as an officer, director or consultant)
                  by a recipient who has attained the age of 55 and who has
                  completed at least five years of service with the Company. If
                  a recipient's employment (or service as an officer, director
                  or consultant) shall terminate because of death or Retirement,
                  the right of the recipient to exercise any option otherwise
                  exercisable on the date of such termination shall be
                  unaffected by such termination and shall continue until the
                  normal expiration of such option. Notwithstanding the
                  foregoing, the tax treatment available pursuant to Section 421
                  of the Code upon the exercise of an incentive stock option
                  will not be available in connection with the exercise of any
                  incentive stock option more than three months after the date
                  of termination of such option recipient's employment due to
                  Retirement. Option rights shall not be affected by any change
                  of employment as long as the recipient continues to be
                  employed by either the Company or a parent or subsidiary of
                  the Company. In no event, however, shall an option be
                  exercisable after the expiration of its original term as
                  determined by the Committee pursuant to subparagraph 6(c)
                  above. The Committee may, if it determines that to do so would
                  be in the Company's best interests, provide in a specific case
                  or cases for the exercise of options which would otherwise
                  terminate upon termination of employment with the Company for
                  any reason, upon such terms and conditions as the Committee
                  determines to be appropriate. Nothing in the Plan or in any
                  option agreement shall confer any right to continue in the
                  employ of the Company or any parent or subsidiary of the
                  Company or interfere in any way with the right of the Company
                  or any parent or subsidiary of the Company to terminate the
                  employment of a recipient at any time.

                           (g)      Leave of Absence. In the case of a recipient
                  on an approved leave of absence, the Committee may, if it
                  determines that to do so would be in the best interests of the
                  Company, provide in a specific case for continuation of
                  options during such leave of absence, such continuation to be
                  on such terms and conditions as the Committee determines to be
                  appropriate, except that in no event shall an option be
                  exercisable after 10 years from the date it is granted.

                           (h)      Recapitalization. In the event that
                  dividends payable in Common Stock during any fiscal year of
                  the Company exceed in the aggregate five percent of the Common
                  Stock issued and outstanding at the beginning of the year, or
                  in the event there is during any fiscal year of the Company
                  one or more splits, subdivisions, or combinations of shares of
                  Common Stock resulting in an increase or decrease by more than
                  five percent of the shares outstanding at the beginning of the
                  year, the number of shares available under the Plan shall be
                  increased or decreased proportionately, as the case may be,
                  and the number of shares deliverable upon the exercise
                  thereafter of any options theretofore granted shall be
                  increased or decreased proportionately, as the case may be,
                  without change in the aggregate purchase price. Common Stock
                  dividends, splits, subdivisions, or combinations during any
                  fiscal year that do not exceed in the aggregate five percent
                  of the Common Stock issued and outstanding at the beginning of
                  such year shall be ignored for purposes of the Plan. All
                  adjustments shall be made as of the day such action
                  necessitating such adjustment becomes effective.

                           (i) Sale or Reorganization. In case the Company is
                  merged or consolidated with another corporation, or in case
                  the property or stock of the Company is acquired by another
                  corporation, or in case of a separation, reorganization, or

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                  liquidation of the Company, the Board of Directors of the
                  Company, or the board of directors of any corporation assuming
                  the obligations of the Company hereunder, shall either (i)
                  make appropriate provisions for the protection of any
                  outstanding options by the substitution on an equitable basis
                  of appropriate stock of the Company, or appropriate options to
                  purchase stock of the merged, consolidated, or otherwise
                  reorganized corporation, provided only that such substitution
                  of options shall, with respect to incentive stock options,
                  comply with the requirements of Section 424(a) of the Code, or
                  (ii) give written notice to optionees that their options,
                  which will become immediately exercisable notwithstanding any
                  waiting period otherwise prescribed by the Committee, must be
                  exercised within 30 days of the date of such notice or they
                  will be terminated.

                           (j)      General Restrictions. Each option granted
                  under the Plan shall be subject to the requirement that, if at
                  any time the Board of Directors shall determine, in its
                  discretion, that the listing, registration, or qualification
                  of the shares issuable or transferable upon exercise thereof
                  upon any securities exchange or under any state or federal
                  law, or the consent or approval of any governmental regulatory
                  body is necessary or desirable as a condition of, or in
                  connection with, the granting of such option or the issue,
                  transfer, or purchase of shares thereunder, such option may
                  not be exercised in whole or in part unless such listing,
                  registration, qualification, consent, or approval shall have
                  been effected or obtained free of any conditions not
                  acceptable to the Board of Directors.

                                    The Company shall not be obligated to sell
                  or issue any shares of Common Stock in any manner in
                  contravention of the Securities Act, the Securities Exchange
                  Act of 1934, as amended (the "Exchange Act"), the rules and
                  regulations of the Securities and Exchange Commission, any
                  state securities law, the rules and regulations promulgated
                  thereunder or the rules and regulations of any securities
                  exchange or over the counter market on which the Common Stock
                  is listed or in which it is included for quotation. The Board
                  of Directors may, in connection with the granting of each
                  option, require the individual to whom the option is to be
                  granted to enter into an agreement with the Company stating
                  that as a condition precedent to each exercise of the option,
                  in whole or in part, he shall, if then required by the
                  Company, represent to the Company in writing that such
                  exercise is for investment only and not with a view to
                  distribution, and also setting forth such other terms and
                  conditions as the Committee may prescribe. Such agreements may
                  also, in the discretion of the Committee, contain provisions
                  requiring the forfeiture of any options granted and/or Common
                  Stock held, in the event of the termination of employment or
                  association, as the case may be, of the optionee with the
                  Company. Upon any forfeiture of Common Stock pursuant to an
                  agreement authorized by the preceding sentence, the Company
                  shall pay consideration for such Common Stock to the optionee,
                  pursuant to any such agreement, without interest thereon.

                           (k)      "Fair Market Value." Fair Market Value for
                  all purposes under the Plan shall mean the closing price of
                  shares of Common Stock, as reported in The Wall Street
                  Journal, in the NASDAQ National Market Issues or similar
                  successor consolidated transactions reports (or a similar
                  consolidated transactions report for the exchange on which the
                  shares of Common Stock are then trading) for the relevant
                  date, or if no sales of shares of Common Stock were made on
                  such date, the average of the

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                  high and low sale prices of shares as reported in such
                  composite transaction report for the preceding day on which
                  sales of shares were made. If the shares are not listed on a
                  national securities exchange or included for quotation in the
                  NASDAQ National Market System at the time Fair Market Value is
                  to be determined, then Fair Market Value shall be determined
                  by the Committee in good faith pursuant to such method as to
                  the Committee deems appropriate and equitable. Under no
                  circumstances shall the Fair Market Value of a share of Common
                  Stock be less than its par value.

7.       Termination and Amendment of the Plan

                  The Board of Directors or the Committee shall have the right
         to amend, suspend, or terminate the Plan at any time; provided,
         however, that no such action shall affect or in any way impair the
         rights of a recipient under any option right theretofore granted under
         the Plan; and, provided, further, that unless first duly approved by
         the stockholders of the Company entitled to vote thereon at a meeting
         (which may be the annual meeting) duly called and held for such
         purpose, except as provided in subparagraphs 6(h) and 6(i), no
         amendment or change shall be made in the Plan increasing the total
         number of shares which may be issued or transferred under the Plan,
         materially increasing the benefits to Plan participants or modifying
         the requirements as to eligibility for participation in the Plan.

8.       Restriction on Sale of Shares

                  Without the written consent of the Company, no stock acquired
         by an optionee upon exercise of an incentive stock option granted
         hereunder may be disposed of by the optionee within two years from the
         date such incentive stock option was granted, nor within one year after
         the transfer of such stock to the optionee; provided, however, that a
         transfer to a trustee, receiver, or other fiduciary in any insolvency
         proceeding, as described in Section 422(c)(3) of the Code, shall not be
         deemed to be such a disposition. The optionee shall make appropriate
         arrangements with the Company for any taxes which the Company is
         obligated to collect in connection with any such disposition, including
         any federal, state, or local withholding taxes.

                  No stock acquired by an optionee upon exercise of a
         non-qualified stock option granted hereunder may be disposed of by the
         optionee (or other person eligible to exercise the option) within six
         months from the date such non-qualified stock option was granted,
         unless otherwise provided by the Committee.

9.       Effective Date of the Plan

                  This Plan is effective as of June 23, 1999, provided, however,
         that the Plan be approved by the stockholders of the Company at the
         2000 Annual Meeting of Stockholders. If the Plan is not approved by the
         stockholders, the Plan and options granted hereunder shall thereupon
         terminate. In any event, the Plan shall terminate on June 22, 2009, or
         on such earlier date as the Board of Directors or the Committee may
         determine. Any option outstanding at the termination date shall remain
         outstanding until it has either expired or has been exercised.

10.      Compliance with Rule 16b-3

                  With respect to persons subject to Section 16 of the Exchange
         Act, transactions under this Plan are intended to comply with all
         applicable conditions of Rule 16b-3 or its successors. To the

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         extent any provision of the Plan or action by the Committee (or any
         other person on behalf of the Committee or the Company) fails to so
         comply, it shall be deemed null and void, to the extent permitted by
         law and deemed advisable by the Committee.

11.      Automatic Grant of Options to Non-Employee Directors

                  The purpose of this Section 11 is to continue the program of
         automatic grants of options to non-employee directors of the Company
         established pursuant to Section 11 of the Company's 1993 Incentive and
         Non-Qualified Stock Option Plan and continued by the Company's 1997
         Incentive and Non-Qualified Stock Option Plan (collectively, the "Prior
         Plans"). The following options, to the extent not heretofore granted
         pursuant to the Prior Plans, shall be automatically awarded:

                           (a)      Each director, who is not also an employee
                  of the Company or any of its affiliates, or the designee of
                  any stockholder of the Company pursuant to a right to
                  designate one or more directors (an "Eligible Director") shall
                  automatically be awarded a grant of 50,000 non-qualified stock
                  options upon his or her initial election to the Board of
                  Directors. Such options shall vest and be exercisable solely
                  in accordance with the following schedule:

                           (i)      The options may be exercised with respect to
                                    a maximum of one-half of the option shares
                                    during the twelve-month period beginning
                                    after the date of grant.

                           (ii)     The options may be exercised with respect to
                                    all of the option shares upon the Eligible
                                    Director's reelection to the Board of
                                    Directors for a second consecutive term.

                           (iii)    The options will expire and will no longer
                                    be exercisable as of the tenth anniversary
                                    of the date of grant, subject to sooner
                                    expiration upon the occurrence of certain
                                    events as provided elsewhere in this Plan.

                           (b)      In addition to the grant provided in
                  subsection (a), each Eligible Director shall automatically be
                  awarded a grant of non-qualified stock options upon the
                  reelection of such Eligible Director to a third or subsequent,
                  successive term, in the amount and at the times hereinafter
                  set forth. Such automatic grants of non-qualified stock
                  options commenced on June 21, 1995, pursuant to the Prior
                  Plans, and have occurred and shall continue to occur annually
                  thereafter on the date of the annual meeting of stockholders
                  for such year until the termination of the Plan. The number of
                  options to which each Eligible Director shall be entitled
                  pursuant to this subsection (b) shall be as follows:

                           (i)      20,000 on the date of the Eligible
                                    Director's reelection to a third one-year
                                    term;

                           (ii)     20,000 on the date of the Eligible
                                    Director's reelection to a fourth one-year
                                    term;

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                           (iii)    15,000 on the date of the Eligible
                                    Director's reelection to a fifth one-year
                                    term;

                           (iv)     15,000 on the date of the Eligible
                                    Director's reelection to a sixth one-year
                                    term;

                           (v)      10,000 on the date of the Eligible
                                    Director's reelection to a seventh one-year
                                    term;

                           (vi)     10,000 on the later of the date of the
                                    annual meeting of stockholders in 2000, or
                                    the date of the Eligible Director's
                                    reelection to an eighth one-year term; and

                           (vii)    10,000 on the later of the date of the
                                    annual meeting of stockholders in 2001, or
                                    the date of the Eligible Director's
                                    reelection to a ninth one-year term.

                  Such options shall vest and be exercisable solely in
                  accordance with the following schedule:

                           (i)      The options shall not be exercisable during
                                    the twelve-month period beginning after the
                                    date of grant.

                           (ii)     The options may be exercised with respect to
                                    one-third of the option shares after the
                                    expiration of twelve months from the date of
                                    grant.

                           (iii)    The remaining two-thirds of the options
                                    shall vest and become exercisable ratably on
                                    a monthly basis over the two-year period
                                    commencing one year from the date of grant
                                    and ending three years from the date of
                                    grant.

                           (iv)     The options will expire and will no longer
                                    be exercisable as of the tenth anniversary
                                    of the date of grant, subject to sooner
                                    expiration upon the occurrence of certain
                                    events as provided elsewhere in this Plan.

                           (c)      The option price for all options awarded
                  under this Section 11 shall be equal to 100% of the Fair
                  Market Value of a share of Common Stock on the date of grant.