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                                                                    EXHIBIT 99.1

                            OSI PHARMACEUTICALS, INC.

                             A Delaware Corporation

                          AMENDED AND RESTATED BY-LAWS

                                    ARTICLE I

                                  STOCKHOLDERS

         Section 1.1 Annual Meeting

         An annual meeting of stockholders for the purpose of electing directors
and of transacting such other business as may come before it shall be held each
year at such date, time, and place, either within or without the State of
Delaware, as may be specified by the Board of Directors.

         Section 1.2 Special Meetings

         Special meetings of stockholders for any purpose or purposes unless
otherwise provided by law or by the Certificate of Incorporation, may be called
at any time by the vote of a majority of the Board of Directors, at such time
and place either within or without the State of Delaware as may be stated in the
notice. Stockholders of the Corporation shall not be entitled to call special
meetings of stockholders.

         Section 1.3 Notice of Meetings

         Written notice of stockholders meetings, stating the place, date, and
hour thereof, and, in the case of a special meeting, the purpose or purposes for
which the meeting is called, shall be given by the Chairman of the Board, if
any, the President, any Vice President, the Secretary, or an Assistant
Secretary, to each stockholder entitled to vote thereat at least ten days but
not more than sixty days before the date of the meeting, unless a different
period is prescribed by law.

         Section 1.4 Quorum

         Except as otherwise provided by law or in the Certificate of
Incorporation or these By-Laws, at any meeting of stockholders, the holders of a
majority of the outstanding shares of each class of stock entitled to vote at
the meeting shall be present or represented by proxy in order to constitute a
quorum for the transaction of any business. In the absence of a quorum, a
majority in interest of the stockholders present or the chairman of the meeting
may adjourn the meeting from time to time in the manner provided in Section 1.5
of these By-Laws until a quorum shall attend.

         Section 1.5 Adjournment

         Any meeting of stockholders, annual or special, may adjourn from time
to time to reconvene at the same or some other place, and notice need not be
given of any such adjourned meeting if the time and place thereof are announced
at the

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meeting at which the adjournment is taken. At the adjourned meeting, the
Corporation may transact any business which might have been transacted at the
original meeting. If the adjournment is for more than thirty days, or if after
the adjournment a new record date is fixed for the adjourned meeting, a notice
of the adjourned meeting shall be given to each stockholder of record entitled
to vote at the meeting.

         Section 1.6 Organization

         The Chairman of the Board, if any, or in his absence the President, or
in their absence any Vice President, shall call to order meetings of
stockholders and shall act as chairman of such meetings. The Board of Directors
or, if the Board fails to act, the stockholders may appoint any stockholder,
director, or officer of the Corporation to act as chairman of any meeting in the
absence of the Chairman of the Board, the President, and all Vice Presidents.

         The Secretary of the Corporation shall act as secretary of all meetings
of stockholders, but, in the absence of the Secretary, the chairman of the
meeting may appoint any other person to act as secretary of the meeting.

         Section 1.7 Voting

         Except as otherwise provided by law or in the Certificate of
Incorporation or these By-Laws and except for the election of directors, at any
meeting duly called and held at which a quorum is present, a majority of the
votes cast at such meeting upon a given question by the holders of outstanding
shares of stock of all classes of stock of the Corporation entitled to vote
thereon who are present in person or by proxy shall decide such question. At any
meeting duly called and held for the election of directors at which a quorum is
present, directors shall be elected by a plurality of the votes cast by the
holders (acting as such) of shares of stock of the Corporation entitled to elect
such directors.

         Section 1.8 Nominations for Election of Directors and Submission of
Proposals

         (a) Nominations for the election of directors at any annual meeting may
be made by the Board of Directors or by any stockholder entitled to vote for the
election of directors. Nominations by a stockholder shall be made by notice in
writing, delivered or mailed, and received by the Secretary of the Corporation
in accordance with paragraph (c). Each notice of nomination submitted by a
stockholder shall set forth (i) the name, age, business address and, if known,
residence address of each nominee proposed in such notice, (ii) the principal
occupation or employment of each such nominee, and (iii) the number of shares of
stock of the Corporation which are beneficially owned by each such nominee.

         (b) Any proposal which a stockholder proposes to make at an annual
meeting of stockholders of the Corporation shall be made by notice in writing,
containing the text of the proposal and a statement that such stockholder
intends to make such proposal at the annual meeting, and which shall be
delivered or mailed, and received by the Secretary of the Corporation in
accordance with paragraph (c).

         (c) Any notice pursuant to paragraph (a) or (b) shall be made at least
45 days prior to the date on

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which the Corporation first mailed its proxy materials for the prior year's
annual meeting of stockholders, or, if the Corporation did not have an annual
meeting of stockholders in the prior year, 90 days prior to the date of the
annual meeting.

                                   ARTICLE II
                               BOARD OF DIRECTORS

         Section 2.1 Number and Term of Office

         The business, property, and affairs of the Corporation shall be managed
by or under the direction of a Board of seven directors provided, however, that
the Board, by resolution adopted by vote of a majority of the then authorized
number of directors, may increase or decrease the number of directors. The
directors shall be elected at the annual meeting of stockholders, and each shall
serve (subject to the provisions of Article IV) until the next succeeding annual
meeting of the stockholders and until his respective successor has been elected
and qualified.

         Section 2.2 Chairman of the Board

         The directors may elect one of their members to be Chairman of the
Board of Directors. The Chairman shall be subject to the control of and may be
removed by the Board of Directors. He shall perform such duties as may from time
to time be assigned to him by the Board.

         Section 2.3 Meetings

         The annual meeting of the Board of Directors, for the election of
officers and the transaction of such other business as may come before the
meeting, shall be held without notice at the same place as, and immediately
following, the annual meeting of the stockholders.

         Regular meetings of the Board of Directors may be held without notice
at such time and place as shall from time to time be determined by the Board.

         Special meetings of the Board of Directors shall be held at such time
and place as shall be designated in the notice of the meeting whenever called by
the Chairman of the Board, if any, the President, or by a majority of the
directors then in office.

         Section 2.4 Notice of Special Meetings

         The secretary, or in his absence any other officer of the Corporation,
shall give each director notice of the time and place of holding of special
meetings of the Board of Directors by mail at least three days before the
meeting, or by telegram, cable, radiogram, or personal service at least one day
before the meeting. Unless otherwise stated in the notice thereof, any and all
business may be transacted at any meeting without specification of such business
in the notice.

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         Section 2.5 Quorum and Organization of Meetings

                  A majority of the total number of members of the Board of
Directors as constituted from time to time shall constitute a quorum for the
transaction of business, but, if at any meeting of the Board of Directors
(whether or not adjourned from a previous meeting) there shall be less than a
quorum present, a majority of those present may adjourn the meeting to another
time and place, and the meeting may be held as adjourned without further notice
or waiver. Except as otherwise provided by law or in the Certificate of
Incorporation or these By-Laws, a majority of the entire Board of Directors may
decide any question brought before such meetings. Meetings shall be presided
over by the Chairman of the Board, if any, or in his absence by the President,
or in the absence of both such other person as the directors may select. The
Secretary of the Corporation shall act as secretary of the meeting, but in his
absence the chairman of the meeting may appoint any person to act as secretary
of the meeting.

         Section 2.6 Committees

         The Board of Directors may, by resolution passed by a majority of the
whole Board, designate one or more committees, each committee to consist of one
or more of the directors of the Corporation. The Board may designate one or more
directors as alternate members of any committee, who may replace any absent or
disqualified member at any meeting of the committee. In the absence or
disqualification of a member of a committee, the member or members thereof
present at any meeting and not disqualified from voting, whether or not he or
they constitute a quorum, may unanimously appoint another member of the Board of
Directors to act at the meeting in place of any such absent or disqualified
member. Any such committee, to the extent provided in the resolution of the
Board of Directors, shall have and may exercise all powers and authority of the
Board of Directors in the management of the business, property, and affairs of
the Corporation, and may authorize the seal of the Corporation to be affixed to
all papers which may require it; but no such committee shall have power or
authority in reference to amending the Certificate of Incorporation of the
Corporation, adopting an agreement of merger or consolidation, recommending to
the stockholders the sale, lease, or exchange of all or substantially all of the
Corporation's property and assets, recommending to the stockholders a
dissolution of the Corporation or a revocation of dissolution, or amending these
By-Laws; and, unless the resolution expressly so provided, no such committee
shall have power or authority to declare a dividend or to authorize the issuance
of stock. Each committee which may be established by the Board of Directors or
these By-Laws may fix its own rules and procedures. Notice of meetings of
committees, other than of regular meetings provided for by the rules, shall be
given to committee members. All action taken by the committees shall be recorded
in minutes of the meetings.

         Section 2.7 Action Without Meeting

         Nothing contained in these By-Laws shall be deemed to restrict the
power of the directors or members of any

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committee to take any action, required or permitted to be taken by them, without
meeting.

         Section 2.8 Telephone Meetings

         Nothing contained in these By-Laws shall be deemed to restrict the
power of members of the Board of Directors, or any committee designated by the
Board, to participate in a meeting of the Board, or committee, by means of
conference telephone or similar communications equipment by means of which all
persons participating in the meeting can hear each other.

                                   ARTICLE III
                                    OFFICERS

         Section 3.1 Executive Officers

         The executive officers of the Corporation shall be a President, a
Scientific Director, one or more Vice Presidents, a Treasurer, and a Secretary,
each of whom shall be elected by the Board of Directors. The Board of Directors
may elect or appoint such other officers (including a Chairman of the Board,
Chief Financial Officer, a Controller and one or more Assistant Treasurers and
Assistant Secretaries) as it may deem necessary or desirable. Each officer shall
hold office for such term as may be prescribed by the Board of Directors from
time to time. Any person may hold at one time two or more offices.

         Section 3.2 Powers and Duties

         The Chairman of the Board, if any, or, in his absence, the President,
shall preside at all meetings of the stockholders and of the Board of Directors.
The President shall be the chief executive officer of the Corporation. In the
absence of the President, a Vice President appointed by the President or, if the
President fails to make such appointment, by the Board, shall perform all the
duties of the President. The officers and agents of the Corporation shall each
have such powers and authority and shall perform such duties in the management
of the business, property, and affairs of the Corporation as generally pertain
to their respective offices, as well as such powers and authorities and such
duties as from time to time may be prescribed by the Board of Directors.

                                   ARTICLE IV
                      RESIGNATIONS, REMOVALS AND VACANCIES

         Section 4.1 Resignations

         Any director or officer of the Corporation, or any member of any
committee, may resign at any time by giving written notice to the Board of
Directors, the President, or the Secretary of the Corporation. Any such
resignation shall take effect at the time specified therein or, if the time be
not specified therein, then upon receipt thereof. The acceptance of such
resignation shall not be necessary to make it effective.

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         Section 4.2 Removals

         The Board of Directors, by a vote of not less than a majority of the
entire Board, at any meeting thereof, or by written consent, at any time, may,
to the extent permitted by law, remove with or without cause from office or
terminate the employment of any officer or member of any committee and may, with
or without cause, disband any committee.

         Any director or the entire Board of Directors may be removed, with or
without cause, by the holders of a majority of the shares entitled at the time
to vote at an election of directors.

         Section 4.3 Vacancies

         Any vacancy in the office of any director or officer through death,
resignation, removal, disqualification, or other cause, and any additional
directorship resulting from increase in the number of directors, may be filled
at any time by a majority of the directors then in office (even though less than
a quorum remains) or, in the case of any vacancy in the office of any director,
by the stockholders, and, subject to the provisions of this Article IV, the
person so chosen shall hold office until his successor shall have been elected
and qualified; or, if the person so chosen is a director elected to fill a
vacancy, he shall (subject to the provisions of this Article IV) hold office for
the unexpired term of his predecessor.

                                    ARTICLE V
                                  CAPITAL STOCK

         Section 5.1 Stock Certificates

         The certificates for share of the capital stock of the Corporation
shall be in such form as shall be prescribed by law and approved, from time to
time, by the Board of Directors.

         Section 5.2 Transfer of Shares

         Shares of the capital stock of the Corporation may be transferred on
the books of the Corporation only by the holder of such shares or by his duly
authorized attorney, upon the surrender to the Corporation or its transfer agent
of the certificate representing such stock properly endorsed.

         Section 5.3 Fixing Record Date

         In order that the Corporation may determine the stockholders entitled
to notice of or to vote at any meeting of stockholders or any adjournment
thereof or to express consent to corporate action in writing without a meeting,
or entitled to receive payment of any dividend or other distribution or
allotment of any rights, or entitled to exercise any rights in respect of any
change, conversion, or exchange of stock, or for the purpose of any other lawful
action, the Board of Directors may fix, in advance, a record date, which, unless
otherwise provided by law, shall not be more than sixty nor less than ten days
before the date of such meeting, nor more than sixty days prior to any other
action.

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         Section 5.4 Lost Certificates

         The Board of Directors or any transfer agent of the Corporation may
direct a new share certificate or certificates to be issued in place of any
certificate or certificates theretofore issued by the Corporation, alleged to
have been lost, stolen, or destroyed, upon the making of an affidavit of that
fact by the person claiming the certificate to be lost, stolen, or destroyed.
When authorizing such issue of a new certificate or certificates, the Board of
Directors may, in its discretion and as a condition precedent to the issuance
thereof, require the owner of such lost, stolen, or destroyed certificate or
certificates, or his legal representative, to give the Corporation bond in such
sum as the Board of Directors shall direct to indemnify the Corporation against
any claim that may be made against the Corporation with respect to the
certificate alleged to have been lost, stolen, or destroyed or the issuance of
such new certificates, and such requirement may be general or confined to
specific instances.

         Section 5.5 Regulations

         The Board of Directors shall have power and authority to make all such
rules and regulations as it may deem expedient concerning the issue, transfer,
registration, cancellation, and replacement of certificates representing stock
of the Corporation.

                                   ARTICLE VI
                                  MISCELLANEOUS

         Section 6.1 Corporate Seal

         The corporate seal shall have inscribed thereon the name of the
Corporation, the year of its organization, and the words "Corporate Seal" and
"Delaware", and shall be in such form as may be approved from time to time by
the Board of Directors.

         Section 6.2 Fiscal Year

         The fiscal year of the Corporation shall be determined by resolution of
the Board of Directors.

         Section 6.3 Notices and Waivers Thereof

         Whenever any notice is required by law, the Certificate of
Incorporation, or these By-Laws to by given to any stockholder, director, or
officer, such notice, except as otherwise provided by law, may be given
personally, or by mail, or in the case of directors or officers, by telegram,
cable, or radiogram, addressed to such address as appears on the books or the
Corporation. Any notice given by telegram, cable, or radiogram shall be deemed
to have been given when it shall have been delivered for transmission and any
notice given by mail shall be deemed to have been given when it shall have been
deposited in the United States mail with postage thereon prepaid.

         Whenever any notice is required to be given by law, the Certificate of
Incorporation, or these By-Laws, a

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written waiver thereof, signed by the person entitled to such notice, whether
before or after the meeting or the time stated therein, shall be deemed
equivalent in all respects to such notice to the full extent permitted by law.

         Section 6.4 Stock of Other Corporations Other Interests

         Unless otherwise ordered by the Board of Directors, the President, the
Secretary, and such attorneys or agents of the Corporation as may be from time
to time authorized by the Board of Directors or the President, shall have full
power and authority on behalf of this Corporation to attend and to act and vote
in person or by proxy at any meeting of the holders of securities of any
corporation or other entity in which this Corporation may own or hold shares or
other securities, and at such meetings shall possess and may exercise all the
rights and powers incident to the ownership of such shares or other securities
which this Corporation, as the owner or holder thereof, might have possessed and
exercised if present. The President, the Secretary or such attorneys or agents,
may also execute and deliver on behalf of the Corporation powers of attorney,
proxies, consents, waivers and other instruments relating to the shares or
securities owned or held by this Corporation.

                                   ARTICLE VII
                                   AMENDMENTS

         The holders of shares entitled at the time to vote for the election of
directors shall have power to adopt, amend, or repeal the By-Laws of the
Corporation by vote of not less than a majority of such shares, and except as
otherwise provided by law, the Board of Directors shall have power equal in all
respects to that of the stockholders to adopt, amend, or repeal the By-Laws by
vote of not less than a majority of the entire Board. However, any By-Law
adopted by the board may be amended or repealed by vote of the holders of a
majority of the shares entitled at the time to vote for the election or
directors.