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                                                                     EXHIBIT 4.4

                                                                  EXECUTION COPY

                          REGISTRATION RIGHTS AGREEMENT

          THIS REGISTRATION RIGHTS AGREEMENT is made and entered into as of
February 1, 2002 by and between OSI Pharmaceuticals, Inc., a Delaware
corporation ("the Company"), and Merrill Lynch & Co., Merrill Lynch, Pierce,
Fenner & Smith Incorporated, Robertson Stephens, Inc., Adams, Harkness & Hill,
Inc. and Lazard Freres & Co. LLC (collectively, the Initial Purchasers, and each
individually, an "Initial Purchaser") pursuant to the Purchase Agreement, dated
January 28, 2002 (the "Purchase Agreement"), between the Company and the Initial
Purchasers. In order to induce the Initial Purchasers to enter into the Purchase
Agreement, the Company has agreed to provide the registration rights set forth
in this Agreement. The execution of this Agreement is a condition to the closing
under the Purchase Agreement.

          The Company agrees with the Initial Purchasers, for its benefit as
Initial Purchasers and for the benefit of the beneficial owners (including the
Initial Purchasers) from time to time of the Registrable Securities (as defined
herein) (each of the foregoing a "Holder" and together the "Holders"), as
follows:

          Section 1.   DEFINITIONS. Capitalized terms used herein without
definition shall have their respective meanings set forth in the Purchase
Agreement. As used in this Agreement, the following terms shall have the
following meanings:

          "AFFILIATE" means, with respect to any specified person, an
"affiliate," as defined in Rule 144, of such person.

          "AMENDMENT EFFECTIVENESS DEADLINE DATE" has the meaning specified in
Section 2(d) hereof.

          "BUSINESS DAY" means each Monday, Tuesday, Wednesday, Thursday and
Friday that is not a day on which banking institutions in The City of New York
are authorized or obligated by law or executive order to close.

          "COMMON STOCK" means the shares of Common Stock, $0.01 par value, of
the Company and any other shares of common stock as may constitute "Common
Stock" for purposes of the Indenture, including the Underlying Common Stock.

          "CONVERSION PRICE" has the meaning assigned to that term in the
Indenture.

          "DAMAGES ACCRUAL PERIOD" has the meaning specified in Section 2(e)
hereof.

          "DAMAGES PAYMENT DATE" means each August 1 and February 1 in the case
of Securities and the Underlying Common Stock.

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          "DEFERRAL NOTICE" has the meaning specified in Section 3(i) hereof.

          "DEFERRAL PERIOD" has the meaning specified in Section 3(i) hereof.

          "EFFECTIVENESS DEADLINE DATE" has the meaning specified in
Section 2(a) hereof.

          "EFFECTIVENESS PERIOD" means the period of two years from the Issue
Date or such shorter period that will terminate upon the earliest of the
following: (A) when all the Securities covered by the Shelf Registration
Statement have been sold pursuant to the Shelf Registration Statement or when
all shares of Underlying Common Stock have been sold pursuant to the Shelf
Registration Statement and (B) when, in the written opinion of counsel to the
Company, all outstanding Registrable Securities held by persons which are not
affiliates of the Company may be resold without registration under the
Securities Act pursuant to Rule 144(k) under the Securities Act or any successor
provision thereto.

          "EVENT" has the meaning specified in Section 2(e) hereof.

          "EVENT TERMINATION DATE" has the meaning specified in Section 2(e)
hereof.

          "EVENT DATE" has the meaning specified in Section 2(e) hereof.

          "EXCHANGE ACT" means the Securities Exchange Act of 1934, as amended,
and the rules and regulations of the SEC promulgated thereunder.

          "FILING DEADLINE DATE" has the meaning specified in Section 2(a)
hereof.

          "HOLDER" has the meaning specified in the second paragraph of this
Agreement.

          "INDENTURE" means the Indenture dated as of the date hereof between
the Company and The Bank of New York, as trustee, pursuant to which the
Securities are being issued.

          "INITIAL PURCHASERS" means Merrill Lynch & Co., Merrill Lynch, Pierce,
Fenner & Smith Incorporated, Robertson Stephens, Inc., Adams, Harkness & Hill,
Inc. and Lazard Freres & Co. LLC.

          "INITIAL SHELF REGISTRATION STATEMENT" has the meaning specified in
Section 2(a) hereof.

          "ISSUE DATE" means February 1, 2002.

          "LIQUIDATED DAMAGES AMOUNT" has the meaning specified in Section 2(e)
hereof.

          "MATERIAL EVENT" has the meaning specified in Section 3(i) hereof.

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          "NOTICE AND QUESTIONNAIRE" means a written notice delivered to the
Company containing substantially the information called for by the Selling
Securityholder Notice and Questionnaire attached as Appendix A to the Offering
Memorandum of the Company dated January 28, 2002 relating to the Securities.

          "NOTICE HOLDER" means, on any date, any Holder that has delivered a
Notice and Questionnaire to the Company on or prior to such date.

          "PRINCIPAL AMOUNT" means, with the respect to the Securities, the
principal amount due on the maturity date as shown on such Securities.

          "PROSPECTUS" means the prospectus included in any Registration
Statement (including, without limitation, a prospectus that discloses
information previously omitted from a prospectus filed as part of an effective
registration statement in reliance upon Rule 415 promulgated under the
Securities Act), as amended or supplemented by any amendment or prospectus
supplement, including post-effective amendments, and all materials incorporated
by reference or explicitly deemed to be incorporated by reference in such
Prospectus.

          "PURCHASE AGREEMENT" has the meaning specified in the first paragraph
of this Agreement.

          "RECORD HOLDER" means, with respect to any Damages Payment Date
relating to any Securities or Underlying Common Stock as to which any Liquidated
Damages Amount has accrued, the registered holder of such Securities or
Underlying Common Stock, as the case may be, 17 days prior to the next
succeeding Damages Payment Date.

          "REGISTRABLE SECURITIES" means the Securities, until such Securities
have been converted or exchanged, and the Underlying Common Stock and any
securities into or for which such securities have been converted or exchanged,
and any security issued with respect thereto upon any stock dividend, split or
similar event until, in the case of any such security, the earliest of (i) its
effective registration under the Securities Act and resale in accordance with
the Registration Statement covering it, (ii) expiration of the holding period
that would be applicable thereto under Rule 144(k) were it not held by an
Affiliate of the Company or (iii) its sale to the public pursuant to Rule 144.

          "REGISTRATION EXPENSES" has the meaning specified in Section 5 hereof.

          "REGISTRATION STATEMENT" means any registration statement of the
Company that covers any of the Registrable Securities pursuant to the provisions
of this Agreement, including the Prospectus, amendments and supplements to such
registration statement, including post-effective amendments, all exhibits, and
all materials incorporated by reference or explicitly deemed to be incorporated
by reference in such registration statement.

          "RESTRICTED SECURITIES" has the meaning assigned to that term in Rule
144.

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          "RULE 144" means Rule 144 under the Securities Act, as such Rule may
be amended from time to time, or any similar rule or regulation hereafter
adopted by the SEC.

          "RULE 144A" means Rule 144A under the Securities Act, as such Rule may
be amended from time to time, or any similar rule or regulation hereafter
adopted by the SEC.

          "SEC" means the U.S. Securities and Exchange Commission and any
successor agency.

          "SECURITIES" means the 4% Convertible Senior Subordinated Notes due
2009 of the Company to be purchased pursuant to the Purchase Agreement.

          "SECURITIES ACT" means the Securities Act of 1933, as amended, and the
rules and regulations promulgated by the SEC thereunder.

          "SHELF REGISTRATION STATEMENT" has the meaning specified in Section
2(a) hereof.

          "SUBSEQUENT SHELF REGISTRATION STATEMENT" has the meaning specified in
Section 2(b) hereof.

          "TIA" means the Trust Indenture Act of 1939, as amended.

          "TRUSTEE" means The Bank of New York (or any successor entity), the
Trustee under the Indenture.

          "UNDERLYING COMMON STOCK" The Common Stock into which the Securities
are convertible or issued upon any such conversion.

          Section 2.   SHELF REGISTRATION.

          (a) The Company shall prepare and file or cause to be prepared and
filed with the SEC, as soon as practicable but in any event by the date (the
"Filing Deadline Date") ninety (90) days after the Issue Date, a Registration
Statement for an offering to be made on a delayed or continuous basis pursuant
to Rule 415 of the Securities Act (a "Shelf Registration Statement") registering
the resale from time to time by Holders thereof of all of the Registrable
Securities (the "Initial Shelf Registration Statement"). The Initial Shelf
Registration Statement shall be on Form S-3 or another appropriate form
permitting registration of such Registrable Securities for resale by such
Holders in accordance with the methods of distribution elected by the Holders
and set forth in the Initial Shelf Registration Statement. The Company shall use
reasonable best efforts to cause the Initial Shelf Registration Statement to be
declared effective under the Securities Act as promptly as is practicable but in
any event by the date (the "Effectiveness Deadline Date") that is one hundred
and eighty (180) days after the Issue Date, and to keep the Initial Shelf
Registration Statement (or any Subsequent Shelf Registration Statement)
continuously effective under the Securities Act until the expiration of the
Effectiveness Period; PROVIDED, HOWEVER, that no Holder shall be entitled to
have the Registrable Securities held by it covered by such Shelf Registration
Statement unless such Holder shall have provided a Notice and Questionnaire in
accordance with Section 2(d) and is in compliance with Section 4. None of

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the Company's security holders (other than the Holders of Registrable
Securities) shall have the right to include any of the Company's securities in
the Shelf Registration Statement.

          (b)   If the Initial Shelf Registration Statement or any Subsequent
Shelf Registration Statement ceases to be effective for any reason at any time
during the Effectiveness Period (other than because all Registrable Securities
registered thereunder shall have been resold pursuant thereto or shall have
otherwise ceased to be Registrable Securities), the Company shall use all
reasonable efforts to obtain the prompt withdrawal of any order suspending the
effectiveness thereof, and in any event shall within thirty (30) days of such
cessation of effectiveness amend the Shelf Registration Statement in a manner
reasonably expected to obtain the withdrawal of the order suspending the
effectiveness thereof, or file an additional Shelf Registration Statement
covering all of the securities that as of the date of such filing are
Registrable Securities (a "Subsequent Shelf Registration Statement"). If a
Subsequent Shelf Registration Statement is filed, the Company shall use all
reasonable efforts to cause the Subsequent Shelf Registration Statement to
become effective as promptly as is practicable after such filing and to keep
such Registration Statement (or subsequent Shelf Registration Statement)
continuously effective until the end of the Effectiveness Period.

          (c)   The Company shall supplement and amend the Shelf Registration
Statement if required by the rules, regulations or instructions applicable to
the registration form used by the Company for such Shelf Registration Statement,
if required by the Securities Act or, to the extent to which the Company does
not reasonably object, as reasonably requested by the Initial Purchasers or by
the Trustee on behalf of the registered Holders.

          (d)   Each Holder of Registrable Securities agrees that if such Holder
wishes to sell Registrable Securities pursuant to a Shelf Registration Statement
and related Prospectus, it will do so only in accordance with this Section 2(d)
and Section 3(i). Each Holder of Registrable Securities wishing to sell
Registrable Securities pursuant to a Shelf Registration Statement and related
Prospectus agrees to deliver a Notice and Questionnaire to the Company at least
three (3) Business Days prior to any intended distribution of Registrable
Securities under the Shelf Registration Statement. From and after the date the
Initial Shelf Registration Statement is declared effective, the Company shall,
as promptly as is practicable after the date a Notice and Questionnaire is
delivered, and in any event within five (5) Business Days after such date, (i)
if required by applicable law, file with the SEC a post-effective amendment to
the Shelf Registration Statement or prepare and, if required by applicable law,
file a supplement to the related Prospectus or a supplement or amendment to any
document incorporated therein by reference or file any other required document
so that the Holder delivering such Notice and Questionnaire is named as a
selling security holder in the Shelf Registration Statement and the related
Prospectus in such a manner as to permit such Holder to deliver such Prospectus
to purchasers of the Registrable Securities in accordance with applicable law
and, if the Company shall file a post-effective amendment to the Shelf
Registration Statement, use all reasonable efforts to cause such post-effective
amendment to be declared effective under the Securities Act as promptly as is
practicable, but in any event by the date (the "Amendment Effectiveness Deadline
Date") that is thirty (30) days after the date such post-effective amendment is
required by this clause to be filed; (ii) provide such Holder copies of any
documents filed pursuant to Section 2(d)(i); and (iii) notify such Holder as
promptly as practicable after the effectiveness under the Securities Act of any
post-effective amendment filed pursuant to Section 2(d)(i);

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PROVIDED that if such Notice and Questionnaire is delivered during a Deferral
Period, the Company shall so inform the Holder delivering such Notice and
Questionnaire and shall take the actions set forth in clauses (i), (ii) and
(iii) above upon expiration of the Deferral Period in accordance with
Section 3(i), PROVIDED, FURTHER, that if under applicable law the Company has
more than one option as to the type or manner of making any such filing, it will
make the required filing or filings in the manner or of a type that is
reasonably expected to result in the earliest availability of the Prospectus for
effecting resales of Registrable Securities. Notwithstanding anything contained
herein to the contrary, the Company shall be under no obligation to name any
Holder that is not a Notice Holder as a selling security holder in any
Registration Statement or related Prospectus; provided, however, that any Holder
that becomes a Notice Holder pursuant to the provisions of Section 2(d) of this
Agreement (whether or not such Holder was a Notice Holder at the time the
Registration Statement was declared effective) shall be named as a selling
security holder in the Registration Statement or related Prospectus in
accordance with the requirements of this Section 2(d).

          (e)   The parties hereto agree that the Holders of Registrable
Securities will suffer damages, and that it would not be feasible to ascertain
the extent of such damages with precision, if (i) the Initial Shelf Registration
Statement has not been filed on or prior to the Filing Deadline Date, (ii) the
Initial Shelf Registration Statement has not been declared effective under the
Securities Act on or prior to the Effectiveness Deadline Date, (iii) the Company
has failed to perform its obligations set forth in Section 2(d) hereof within
the time period required therein, (iv) the aggregate duration of Deferral
Periods in any period exceeds the number of days permitted in respect of such
period pursuant to Section 3(i) hereof or (v) the number of Deferral Periods in
any period exceeds the number permitted in respect of such period pursuant to
Section 3(i) (each of the events of a type described in any of the foregoing
clauses (i) through (v) are individually referred to herein as an "Event," and
the Filing Deadline Date in the case of clause (i), the Effectiveness Deadline
Date in the case of clause (ii), the date by which the Company is required to
perform its obligations set forth in Section 2(d) in the case of clause (iii)
(including the filing of any post-effective amendment prior to the Amendment
Effectiveness Deadline Date), the date on which the aggregate duration of
Deferral Periods in any period exceeds the number of days permitted by
Section 3(i) hereof in the case of clause (iv), and the date of the commencement
of a Deferral Period that causes the limit on the number of Deferral Periods in
any period under Section 3(i) hereof to be exceeded in the case of clause (v),
being referred to herein as an "Event Date"). Events shall be deemed to continue
until the "Event Termination Date," which shall be the following dates with
respect to the respective types of Events: the date the Initial Shelf
Registration Statement is filed in the case of an Event of the type described in
clause (i), the date the Initial Shelf Registration Statement is declared
effective under the Securities Act in the case of an Event of the type described
in clause (ii), the date the Company performs its obligations set forth in
Section 2(d) in the case of an Event of the type described in clause (iii)
(including, without limitation, the date the relevant post-effective amendment
to the Shelf Registration Statement is declared effective under the Securities
Act), termination of the Deferral Period that caused the limit on the aggregate
duration of Deferral Periods in a period set forth in Section 3(i) to be
exceeded in the case of the commencement of an Event of the type described in
clause (iv), and termination of the Deferral Period the commencement of which
caused the number of Deferral Periods in a period permitted by Section 3(i) to
be exceeded in the case of an Event of the type described in clause (v).

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          Accordingly, commencing on (and including) any Event Date and ending
on (but excluding) the next date on which there are no Events that have occurred
and are continuing (a "Damages Accrual Period"), the Company agrees to pay, as
liquidated damages and not as a penalty, an amount (the "Liquidated Damages
Amount"), payable on the Damages Payment Dates to Record Holders, accruing for
each portion of such Damages Accrual Period beginning on and including a Damages
Payment Date (or, in respect of the first time that the Liquidation Damages
Amount is to be paid to Holders on a Damages Payment Date as a result of the
occurrence of any particular Event, from the Event Date) and ending on but
excluding the first to occur of (A) the date of the end of the Damages Accrual
Period or (B) the Next Damages Payment Date, at a rate per annum equal to
one-quarter of one percent (0.25%) for the first 90-day period from the Event
Date, and thereafter at a rate per annum equal to one-half of one percent
(0.5%), of the aggregate Principal Amount of such Securities or, if the Holder
has converted such Securities into Underlying Common Stock and such shares of
Common Stock then constitute Registrable Securities, the Conversion Price of
such Securities in effect at the time of such conversion, in each case,
determined as of the Business Day immediately preceding the next Damages Payment
Date; provided, that any Liquidated Damages Amount accrued with respect to any
Securities or portion thereof called for redemption on a redemption date or
converted into Underlying Common Stock on a conversion date prior to the Damages
Payment Date, shall, in any such event, be paid instead to the Holder who
submitted such Securities or portion thereof for redemption or conversion on the
applicable redemption date or conversion date, as the case may be, on such date
(or promptly following the conversion date, in the case of conversion).
Notwithstanding the foregoing, no Liquidated Damages Amounts shall accrue as to
any Registrable Security from and after the earlier of (x) the date such
security is no longer a Registrable Security and (y) expiration of the
Effectiveness Period. The rate of accrual of the Liquidated Damages Amount per
year shall not exceed the 0.5% notwithstanding the occurrence of multiple
concurrent Events. Following the cure of all Events requiring the payment by the
Company of Liquidated Damages Amounts to the Holders of Registrable Securities
pursuant to this Section, the accrual of Liquidated Damages Amounts will cease
(without in any way limiting the effect of any subsequent Event requiring the
payment of Liquidated Damages Amount by the Company).

          The Trustee shall be entitled, on behalf of Holders of Securities or
Underlying Common Stock, to seek any available remedy for the enforcement of
this Agreement, including for the payment of any Liquidated Damages Amount.
Nothing shall preclude a Notice Holder or Holder of Registrable Securities from
pursuing or obtaining specific performance or other equitable relief with
respect to this Agreement.

          All of the Company's obligations set forth in this Section 2(e) that
are outstanding with respect to any Registrable Security at the time such
security ceases to be a Registrable Security shall survive until such time as
all such obligations with respect to such security have been satisfied in full
(notwithstanding termination of this Agreement pursuant to Section 8(k)).

          The parties hereto agree that the liquidated damages provided for in
this Section 2(e) constitute a reasonable estimate of the damages that may be
incurred by Holders of Registrable Securities by reason of the failure of the
Shelf Registration Statement to be filed or

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declared effective or available for effecting resales of Registrable Securities
in accordance with the provisions hereof.

          Section 3.   REGISTRATION PROCEDURES. In connection with the
registration obligations of the Company under Section 2 hereof, the Company
shall:

          (a)   Before filing any Registration Statement or Prospectus or any
amendments or supplements thereto with the SEC, furnish to the Initial
Purchasers copies of all such documents proposed to be filed and use reasonable
efforts to reflect in each such document when so filed with the SEC such
comments as the Initial Purchasers reasonably shall propose within three (3)
Business Days of the delivery of such copies to the Initial Purchasers.

          (b)   Prepare and file with the SEC such amendments and post-effective
amendments to each Registration Statement as may be necessary to keep such
Registration Statement continuously effective for the applicable period
specified in Section 2(a); cause the related Prospectus to be supplemented by
any required Prospectus supplement, and as so supplemented to be filed pursuant
to Rule 424 (or any similar provisions then in force) under the Securities Act;
and use all reasonable efforts to comply with the provisions of the Securities
Act applicable to it with respect to the disposition of all securities covered
by such Registration Statement during the Effectiveness Period in accordance
with the intended methods of disposition by the sellers thereof set forth in
such Registration Statement as so amended or such Prospectus as so supplemented.

          (c)   As promptly as practicable give notice to the Notice Holders and
the Initial Purchasers (i) when any Prospectus, Prospectus supplement,
Registration Statement or post-effective amendment to a Registration Statement
has been filed with the SEC and, with respect to a Registration Statement or any
post-effective amendment, when the same has been declared effective, (ii) of any
request, following the effectiveness of the Initial Shelf Registration Statement
under the Securities Act, by the SEC or any other federal or state governmental
authority for amendments or supplements to any Registration Statement or related
Prospectus or for additional information, (iii) of the issuance by the SEC or
any other federal or state governmental authority of any stop order suspending
the effectiveness of any Registration Statement or the initiation or threatening
of any proceedings for that purpose, (iv) of the receipt by the Company of any
notification with respect to the suspension of the qualification or exemption
from qualification of any of the Registrable Securities for sale in any
jurisdiction or the initiation or threatening of any proceeding for such
purpose, (v) of the occurrence of (but not the nature of or details concerning)
a Material Event (provided, however, that no notice by the Company shall be
required pursuant to this clause (v) in the event that the Company either
promptly files a Prospectus supplement to update the Prospectus or a Form 8-K or
other appropriate Exchange Act report that is incorporated by reference into the
Registration Statement, which, in either case, contains the requisite
information with respect to such Material Event that results in such
Registration Statement no longer containing any untrue statement of material
fact or omitting to state a material fact necessary to make the statements
contained therein not misleading) and (vi) of the determination by the Company
that a post-effective amendment to a Registration Statement will be filed with
the SEC, which notice may, at the discretion of the Company (or as required
pursuant to Section 3(i)), state that it constitutes a Deferral Notice, in which
event the provisions of Section 3(i) shall apply.

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          (d)   Use all reasonable efforts to obtain the withdrawal of any order
suspending the effectiveness of a Registration Statement or the lifting of any
suspension of the qualification (or exemption from qualification) of any of the
Registrable Securities for sale in any jurisdiction in which they have been
qualified for sale, in either case at the earliest possible moment.

          (e)   If reasonably requested by the Initial Purchasers or any Notice
Holder, promptly as reasonably practicable incorporate in a Prospectus
supplement or post-effective amendment to a Registration Statement such
information as the Initial Purchasers or such Notice Holder shall, on the basis
of an opinion of nationally-recognized counsel experienced in such matters,
determine to be required to be included therein by applicable law and make any
required filings of such Prospectus supplement or such post-effective amendment;
provided, that the Company shall not be required to take any actions under this
Section 3(e) that are not, in the reasonable opinion of counsel for the Company,
in compliance with applicable law.

          (f)   As promptly as practicable furnish to each Notice Holder and the
Initial Purchasers, upon their request and without charge, at least one (1)
conformed copy of the Registration Statement and any amendment thereto,
including financial statements but excluding schedules, all documents
incorporated or deemed to be incorporated therein by reference and all exhibits
(unless requested in writing to the Company by such Notice Holder or the Initial
Purchasers, as the case may be).

          (g)   During the Effectiveness Period, deliver to each Notice Holder
in connection with any sale of Registrable Securities pursuant to a Registration
Statement, without charge, as many copies of the Prospectus or Prospectuses
relating to such Registrable Securities (including each preliminary prospectus)
and any amendment or supplement thereto as such Notice Holder may reasonably
request; and the Company hereby consents (except during such periods that a
Deferral Notice is outstanding and has not been revoked) to the use of such
Prospectus or each amendment or supplement thereto by each Notice Holder in
connection with any offering and sale of the Registrable Securities covered by
such Prospectus or any amendment or supplement thereto in the manner set forth
therein.

          (h)   Prior to any public offering of the Registrable Securities
pursuant to the Shelf Registration Statement, use all reasonable efforts to
register or qualify or cooperate with the Notice Holders in connection with the
registration or qualification (or exemption from such registration or
qualification) of such Registrable Securities for offer and sale under the
securities or Blue Sky laws of such jurisdictions within the United States as
any Notice Holder reasonably requests in writing (which request may be included
in the Notice and Questionnaire); prior to any public offering of the
Registrable Securities pursuant to the Shelf Registration Statement, use all
reasonable efforts to keep each such registration or qualification (or exemption
therefrom) effective during the Effectiveness Period in connection with such
Notice Holder's offer and sale of Registrable Securities pursuant to such
registration or qualification (or exemption therefrom) and do any and all other
acts or things necessary or advisable to enable the disposition in such
jurisdictions of such Registrable Securities in the manner set forth in the
relevant Registration Statement and the related Prospectus; provided, that the
Company will not be required to (i) qualify as a foreign corporation or as a
dealer in securities in any jurisdiction where it would not otherwise be
required to qualify but for this Agreement or (ii) take any action that would

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subject it to general service of process in suits or to taxation in any such
jurisdiction where it is not then so subject.

          (i)   Upon (A) the issuance by the SEC of a stop order suspending the
effectiveness of the Shelf Registration Statement or the initiation of
proceedings with respect to the Shelf Registration Statement under Section 8(d)
or 8(e) of the Securities Act, (B) the occurrence of any event or the existence
of any fact (a "Material Event") as a result of which any Registration Statement
shall contain any untrue statement of a material fact or omit to state any
material fact required to be stated therein or necessary to make the statements
therein not misleading, or any Prospectus shall contain any untrue statement of
a material fact or omit to state any material fact required to be stated therein
or necessary to make the statements therein, in the light of the circumstances
under which they were made, not misleading, or (C) the occurrence or existence
of any pending corporate development that, in the discretion of the Company,
makes it appropriate to suspend the availability of the Shelf Registration
Statement and the related Prospectus, (i) in the case of clause (B) above,
subject to the next sentence, as promptly as practicable prepare and file a
post-effective amendment to such Registration Statement or a supplement to the
related Prospectus or any document incorporated therein by reference or file any
other required document that would be incorporated by reference into such
Registration Statement and Prospectus so that such Registration Statement does
not contain any untrue statement of a material fact or omit to state any
material fact required to be stated therein or necessary to make the statements
therein not misleading, and such Prospectus does not contain any untrue
statement of a material fact or omit to state any material fact required to be
stated therein or necessary to make the statements therein, in the light of the
circumstances under which they were made, not misleading, as thereafter
delivered to the purchasers of the Registrable Securities being sold thereunder,
and, in the case of a post-effective amendment to a Registration Statement,
subject to the next sentence, use all reasonable efforts to cause it to be
declared effective as promptly as is reasonably practicable, and (ii) give
notice to the Notice Holders that the availability of the Shelf Registration
Statement is suspended (a "Deferral Notice") and, upon receipt of any Deferral
Notice, each Notice Holder agrees not to sell any Registrable Securities
pursuant to the Registration Statement until such Notice Holder's receipt of
copies of the supplemented or amended Prospectus provided for in clause (i)
above, or until it is advised in writing by the Company that the Prospectus may
be used, and has received copies of any additional or supplemental filings that
are incorporated or deemed incorporated by reference in such Prospectus. The
Company will use all reasonable efforts to ensure that the use of the Prospectus
may be resumed (x) in the case of clause (A) above, as promptly as is
practicable, (y) in the case of clause (B) above, as soon as, in the sole
judgment of the Company, public disclosure of such Material Event would not be
prejudicial to or contrary to the interests of the Company or, if necessary to
avoid unreasonable burden or expense, as soon as reasonably practicable
thereafter and (z) in the case of clause (C) above, as soon as, in the
discretion of the Company, such suspension is no longer appropriate. The period
during which the availability of the Registration Statement and any Prospectus
is suspended (the "Deferral Period") shall, without the Company incurring any
obligation to pay liquidated damages pursuant to Section 2(e), not exceed thirty
(30) days in any three (3) month period or ninety (90) days in any twelve (12)
month period.

          (j)   If reasonably requested in writing in connection with a
disposition of Registrable Securities pursuant to a Registration Statement, make
reasonably available for

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inspection during normal business hours by a representative for the Notice
Holders of such Registrable Securities and any broker-dealers, attorneys and
accountants retained by such Notice Holders, all relevant financial and other
records, pertinent corporate documents and properties of the Company and its
subsidiaries, and cause the appropriate executive officers, directors and
designated employees of the Company and its subsidiaries to make reasonably
available for inspection during normal business hours all relevant information
reasonably requested by such representative for the Notice Holders or any such
broker-dealers, attorneys or accountants in connection with such disposition, in
each case as is customary for similar "due diligence" examinations; provided,
however, that such persons shall first agree in writing with the Company that
any information that is reasonably and in good faith designated by the Company
in writing as confidential at the time of delivery of such information shall be
kept confidential by such persons and shall be used solely for the purposes of
exercising rights under this Agreement, unless (i) disclosure of such
information is required by court or administrative order or is necessary to
respond to inquiries of regulatory authorities, (ii) disclosure of such
information is required by law (including any disclosure requirements pursuant
to federal securities laws in connection with the filing of any Registration
Statement or the use of any Prospectus referred to in this Agreement), (iii)
such information becomes generally available to the public other than as a
result of a disclosure or failure to safeguard by any such person or (iv) such
information becomes available to any such person from a source other than the
Company and such source is not bound by a confidentiality agreement; and
PROVIDED FURTHER, that the foregoing inspection and information gathering shall,
to the greatest extent possible, be coordinated on behalf of all the Notice
Holders and the other parties entitled thereto by the counsel referred to in
Section 5.

          (k)   Comply with all applicable rules and regulations of the SEC and
make generally available to its securityholders earning statements (which need
not be audited) satisfying the provisions of Section 11(a) of the Securities Act
and Rule 158 thereunder (or any similar rule promulgated under the Securities
Act) no later than 45 days after the end of any 12-month period (or 90 days
after the end of any 12-month period if such period is a fiscal year) commencing
on the first day of the first fiscal quarter of the Company commencing after the
effective date of a Registration Statement, which statements shall cover said
12-month periods.

          (l)   Cooperate with each Notice Holder to facilitate the timely
preparation and delivery of certificates representing Registrable Securities
sold pursuant to a Registration Statement, and cause such Registrable Securities
to be in such denominations as are permitted by the Indenture and registered in
such names as such Notice Holder may request in writing at least two Business
Days prior to any sale of such Registrable Securities.

          (m)   Provide a CUSIP number for all Registrable Securities covered by
each Registration Statement not later than the effective date of such
Registration Statement and provide the Trustee for the Securities and the
transfer agent for the Common Stock with printed certificates for the
Registrable Securities that are in a form eligible for deposit with The
Depository Trust Company.

          (n)   Make a reasonable effort to provide such information as is
required for any filings required to be made with the National Association of
Securities Dealers, Inc.

                                       11
<Page>

          (o)   Upon (i) the filing of the Initial Shelf Registration Statement
and (ii) the effectiveness of the Initial Shelf Registration Statement, announce
the same, in each case by release to Reuters Economic Services and Bloomberg
Business News.

          (p)   Enter into such customary agreements and take all such other
reasonable necessary actions in connection therewith (including those reasonably
requested by the holders of a majority of the Registrable Securities being sold)
in order to expedite or facilitate disposition of such Registrable Securities.

          (q)   Cause the Indenture to be qualified under the TIA not later than
the effective date of any Registration Statement; and in connection therewith,
cooperate with the Trustee to effect such changes to the Indenture as may be
required for the Indenture to be so qualified in accordance with the terms of
the TIA and execute, and use all reasonable efforts to cause the Trustee to
execute, all documents as may be required to effect such changes, and all other
forms and documents required to be filed with the SEC to enable the Indenture to
be so qualified in a timely manner.

          Section 4.   HOLDER'S OBLIGATIONS. Each Holder agrees, by acquisition
of the Registrable Securities, that no Holder of Registrable Securities shall be
entitled to sell any of such Registrable Securities pursuant to a Registration
Statement or to receive a Prospectus relating thereto, unless such Holder has
furnished the Company with a Notice and Questionnaire as required pursuant to
Section 2(d) hereof (including the information required to be included in such
Notice and Questionnaire) and the information set forth in the next sentence.
Each Notice Holder agrees promptly to furnish to the Company all information
required to be disclosed in order to make the information previously furnished
to the Company by such Notice Holder not misleading and any other information
regarding such Notice Holder and the distribution of such Registrable Securities
as may be required to be disclosed in the Registration Statement under
applicable law.

          Section 5.   REGISTRATION EXPENSES. The Company shall bear all fees
and expenses incurred in connection with the performance by the Company of its
obligations under Sections 2 and 3 of this Agreement whether or not any of the
Registration Statements are declared effective. Such fees and expenses shall
include, without limitation, (i) all registration and filing fees (including,
without limitation, fees and expenses (x) with respect to filings required to be
made with the National Association of Securities Dealers, Inc. and (y) of
compliance with federal and state securities or Blue Sky laws (including,
without limitation, reasonable fees and disbursements of the counsel specified
in the next sentence in connection with Blue Sky qualifications of the
Registrable Securities under the laws of such jurisdictions as the Notice
Holders of a majority of the Registrable Securities being sold pursuant to a
Registration Statement may designate), (ii) printing expenses (including,
without limitation, expenses of printing certificates for Registrable Securities
in a form eligible for deposit with The Depository Trust Company), (iii)
duplication expenses relating to copies of any Registration Statement or
Prospectus delivered to any Holders hereunder, (iv) fees and disbursements of
counsel for the Company in connection with the Shelf Registration Statement, and
(v) reasonable fees and disbursements of the Trustee and its counsel and of the
registrar and transfer agent for the Common Stock. In addition, the Company
shall bear or reimburse the Notice Holders for the reasonable fees and
disbursements of one firm of legal counsel for the Holders, which shall

                                       12
<Page>

initially be Shearman & Sterling, but which may, upon the written consent of the
Initial Purchasers (which shall not be unreasonably withheld), be another
nationally recognized law firm experienced in securities law matters designated
by the Company. In addition, the Company shall pay the internal expenses of the
Company (including, without limitation, all salaries and expenses of officers
and employees performing legal or accounting duties), the expense of any annual
audit, the fees and expenses incurred in connection with the listing of the
Registrable Securities on any securities exchange on which similar securities of
the Company are then listed and the fees and expenses of any person, including
special experts, retained by the Company.

          Section 6.   INDEMNIFICATION; CONTRIBUTION.

          (a)   The Company agrees to indemnify and hold harmless the Initial
Purchasers and each holder of Registrable Securities and each person, if any,
who controls the Initial Purchasers or any holder of Registrable Securities
within the meaning of either Section 15 of the Securities Act or Section 20 of
the Exchange Act, as follows:

          (i)   against any and all loss, liability, claim, damage and expense
     whatsoever, as incurred, arising out of any untrue statement or alleged
     untrue statement of a material fact contained in the Registration Statement
     (or any amendment thereto), or the omission or alleged omission therefrom
     of a material fact necessary in order to make the statements therein, in
     light of the circumstances under which they were made, not misleading or
     arising out of any untrue statement or alleged untrue statement of a
     material fact included in any preliminary prospectus or the Prospectus (or
     any amendment or supplement thereto), or the omission or alleged omission
     therefrom of a material fact necessary in order to make the statements
     therein, in the light of the circumstances under which they were made, not
     misleading;

          (ii)  against any and all loss, liability, claim, damage and expense
     whatsoever, as incurred, to the extent of the aggregate amount paid in
     settlement of any litigation, or any investigation or proceeding by any
     governmental agency or body, commenced or threatened, or of any claim
     whatsoever based upon any such untrue statement or omission, or any such
     alleged untrue statement or omission, provided that (subject to Section
     6(d) below) any such settlement is effected with the prior written consent
     of the Company; and

          (iii) against any and all expense whatsoever, as incurred (including
     the fees and disbursements of counsel), reasonably incurred in
     investigating, preparing or defending against any litigation, or any
     investigation or proceeding by any governmental agency or body, commenced
     or threatened, or any claim whatsoever based upon any such untrue statement
     or omission, or any such alleged untrue statement or omission, to the
     extent that any such expense is not paid under (i) or (ii) above;

PROVIDED, HOWEVER, that this indemnity shall not apply to any loss, liability,
claim, damage or expense to the extent arising out of any untrue statement or
omission or alleged untrue statement or omission made in reliance upon and in
conformity with information furnished to the Company by each and any Initial
Purchaser or such holder of Registrable Securities (which also

                                       13
<Page>

acknowledges the indemnity provisions herein) and each person, if any, who
controls any such Initial Purchaser or any such holder of Registrable Securities
expressly for use in the Registration Statement (or any amendment thereto), or
any preliminary prospectus or the Prospectus (or any amendment or supplement
thereto).

          (b)   In connection with any Shelf Registration in which a holder,
including, without limitation, each Initial Purchaser, of Registrable Securities
is participating, in furnishing information relating to such holder of
Registrable Securities to the Company expressly for use in such Registration
Statement, any preliminary prospectus, the Prospectus or any amendments or
supplements thereto, the holders of such Registrable Securities agree, severally
and not jointly, to indemnify and hold harmless each Initial Purchaser and each
person, if any, who controls any Initial Purchaser within the meaning of either
Section 15 of the Securities Act or Section 20 of the Exchange Act and the
Company, and each person, if any, who controls the Company within the meaning of
either such Section, against any and all loss, liability, claim, damage and
expense described in the indemnity contained in subsection (a) of this Section,
as incurred, but only with respect to untrue statements or omissions, or alleged
untrue statements or omissions, made in the Registration Statement (or any
amendment thereto), or any preliminary prospectus or the Prospectus (or any
amendment or supplement thereto) in reliance upon and in conformity with written
information furnished to the Company by such holder of Registrable Securities
(which also acknowledges the indemnity provisions herein) and each person, if
any, who controls any such holder of Registrable Securities expressly for use in
the Registration Statement (or any amendment thereto) or such preliminary
prospectus or the Prospectus (or any amendment or supplement thereto).

          Each of the Initial Purchasers agrees to indemnify and hold harmless
the Company, the holders of Registrable Securities, and each person, if any, who
controls the Company or any holder of Registrable Securities within the meaning
of either Section 15 of the Securities Act or Section 20 of the Exchange Act
against any and all loss, liability, claim, damage and expense described in the
indemnity contained in subsection (a) of this Section, as incurred, but only
with respect to untrue statements or omissions, or alleged untrue statements or
omissions, made in the Registration Statement (or any amendment thereto), or any
preliminary prospectus or the Prospectus (or any amendment or supplement
thereto) in reliance upon and in conformity with information furnished to the
Company by such Initial Purchaser expressly for use in the Registration
Statement (or any amendment thereto) or such preliminary prospectus or the
Prospectus (or any amendment or supplement thereto).

          (c)   Each indemnified party shall give notice as promptly as
reasonably practicable to each indemnifying party of any action commenced
against it in respect of which indemnity may be sought hereunder, but failure to
so notify an indemnifying party shall not relieve such indemnifying party from
any liability hereunder to the extent it is not materially prejudiced as a
result thereof and in any event shall not relieve it from any liability which it
may have otherwise than on account of this indemnity agreement. An indemnifying
party may participate at its own expense in the defense of any such action;
PROVIDED, HOWEVER, that counsel to the indemnifying party shall not (except with
the consent of the indemnified party) also be counsel to the indemnified party.
In no event shall the indemnifying parties be liable for fees and expenses of
more than one counsel (in addition to any local counsel) separate from their own
counsel for all indemnified parties in connection with any one action or
separate but similar or

                                       14
<Page>

related actions in the same jurisdiction arising out of the same general
allegations or circumstances. No indemnifying party shall, without the prior
written consent of the indemnified parties, settle or compromise or consent to
the entry of any judgment with respect to any litigation, or any investigation
or proceeding by any governmental agency or body, commenced or threatened, or
any claim whatsoever in respect of which indemnification or contribution could
be sought under this Section 6 hereof (whether or not the indemnified parties
are actual or potential parties thereto), unless such settlement, compromise or
consent (i) includes an unconditional release of each indemnified party from all
liability arising out of such litigation, investigation, proceeding or claim and
(ii) does not include a statement as to or an admission of fault, culpability or
a failure to act by or on behalf of any indemnified party.

          (d)   If at any time an indemnified party shall have requested an
indemnifying party to reimburse the indemnified party for fees and expenses of
counsel, such indemnifying party agrees that it shall be liable for any
settlement of the nature contemplated by Section 6(a)(ii) effected without its
written consent if (i) such settlement is entered into more than 45 days after
receipt by such indemnifying party of aforesaid request, (ii) such indemnifying
party shall have received notice of the terms of such settlement at least 30
days prior to such settlement being entered into and (iii) such indemnifying
party shall not have reimbursed such indemnified party in accordance with such
request for fees and expenses prior to the date of such settlement.

          (e)   If the indemnification provided for in this Section 6 is for any
reason unavailable to or insufficient to hold harmless an indemnified party in
respect of any losses, liabilities, claims, damages or expenses referred to
therein, then each indemnifying party shall contribute to the aggregate amount
of such losses, liabilities, claims, damages and expenses incurred by such
indemnified party, as incurred, in such proportion as is appropriate to reflect
the relative fault of the indemnifying party or parties on the one hand and of
the indemnified party on the other hand in connection with the statements or
omissions which resulted in such losses, liabilities, claims, damages or
expenses, as well as any other relevant equitable considerations.

          The relative fault of the Company on the one hand and the holders of
the Registrable Securities or such Initial Purchaser on the other hand shall be
determined by reference to, among other things, whether any such untrue or
alleged untrue statement of a material fact or omission or alleged omission to
state a material fact relates to information supplied by the Company or by the
holder of the Registrable Securities or such Initial Purchaser and the parties'
relative intent, knowledge, access to information and opportunity to correct or
prevent such statement or omission.

          The parties hereto agree that it would not be just and equitable if
contribution pursuant to this Section 6(e) were determined by pro rata
allocation or by any other method of allocation which does not take account of
the equitable considerations referred to above in this Section 6(e). The
aggregate amount of losses, liabilities, claims, damages, and expenses incurred
by an indemnified party and referred to above in this Section 6(e) shall be
deemed to include any legal or other expenses reasonably incurred by such
indemnified party in investigating, preparing or defending against any
litigation, or any investigation or proceeding by any governmental agency or
body, commenced or threatened, or any claim whatsoever based upon any such
untrue or alleged untrue statement or omission or alleged omission.

                                       15
<Page>

          Notwithstanding the provisions of this Section 6, neither the holder
of any Registrable Securities nor any Initial Purchaser, shall be required to
indemnify or contribute any amount in excess of the amount by which the total
price at which the Registrable Securities sold by such holder of Registrable
Securities or unwritten by such Initial Purchaser, as the case may be, and
distributed to the public were offered to the public exceeds the amount of any
damages that such holder of Registrable Securities or such Initial Purchaser
have otherwise been required to pay by reason of such untrue or alleged untrue
statement or omission or alleged omission.

          No person guilty of fraudulent misrepresentation (within the meaning
of Section 11(f) of the Securities Act) shall be entitled to contribution from
any person who was not guilty of such fraudulent misrepresentation.

          For purposes of this Section 6(e), each person, if any, who controls
any Initial Purchaser or any holder of Registrable Securities within the meaning
of Section 15 of the Securities Act or Section 20 of the Exchange Act shall have
the same rights to contribution as such Initial Purchaser or such holder, and
each person, if any, who controls the Company within the meaning of Section 15
of the Securities Act or Section 20 of the Exchange Act shall have the same
rights to contribution as the Company.

          Section 7.   INFORMATION REQUIREMENTS. The Company covenants that, if
at any time before the end of the Effectiveness Period the Company is not
subject to the reporting requirements of the Exchange Act, it will cooperate
with any Holder of Registrable Securities and take such further reasonable
action as any Holder of Registrable Securities may reasonably request in writing
(including, without limitation, making such reasonable representations as any
such Holder may reasonably request), all to the extent required from time to
time to enable such Holder to sell Registrable Securities without registration
under the Securities Act within the limitation of the exemptions provided by
Rule 144 and Rule 144A under the Securities Act and customarily taken in
connection with sales pursuant to such exemptions. Upon the written request of
any Holder of Registrable Securities, the Company shall deliver to such Holder a
written statement as to whether it has complied with such filing requirements,
unless such a statement has been included in the Company's most recent report
required to be filed and filed pursuant to Section 13 or Section 15(d) of
Exchange Act. Notwithstanding the foregoing, nothing in this Section 7 shall be
deemed to require the Company to register any of its securities (other than
Common Stock) under any section of the Exchange Act.

          Section 8.   MISCELLANEOUS.

          (a)   NO CONFLICTING AGREEMENTS. The Company is not, as of the date
hereof, a party to, nor shall it, on or after the date of this Agreement, enter
into, any agreement with respect to its securities that conflicts with the
rights granted to the Holders of Registrable Securities in this Agreement. The
Company represents and warrants that the rights granted to the Holders of
Registrable Securities hereunder do not in any way conflict with the rights
granted to the holders of the Company's securities under any other agreements.

          (b)   AMENDMENTS AND WAIVERS. The provisions of this Agreement,
including the provisions of this sentence, may not be amended, modified or
supplemented, and waivers or

                                       16
<Page>

consents to departures from the provisions hereof may not be given, unless the
Company has obtained the written consent of Holders of a majority of the then
outstanding Underlying Common Stock constituting Registrable Securities (with
Holders of Securities deemed to be the Holders, for purposes of this Section, of
the number of outstanding shares of Underlying Common Stock into which such
Securities are or would be convertible or exchangeable as of the date on which
such consent is requested). Notwithstanding the foregoing, a waiver or consent
to depart from the provisions hereof with respect to a matter that relates
exclusively to the rights of Holders of Registrable Securities whose securities
are being sold pursuant to a Registration Statement and that does not directly
or indirectly affect the rights of other Holders of Registrable Securities may
be given by Holders of at least a majority of the Registrable Securities being
sold by such Holders pursuant to such Registration Statement; provided, that the
provisions of this sentence may not be amended, modified, or supplemented except
in accordance with the provisions of the immediately preceding sentence. Each
Holder of Registrable Securities outstanding at the time of any such amendment,
modification, supplement, waiver or consent or thereafter shall be bound by any
such amendment, modification, supplement, waiver or consent effected pursuant to
this Section 8(b), whether or not any notice, writing or marking indicating such
amendment, modification, supplement, waiver or consent appears on the
Registrable Securities or is delivered to such Holder.

          (c)   NOTICES. All notices and other communications provided for or
permitted hereunder shall be made in writing by hand delivery, by telecopier, by
courier guaranteeing overnight delivery or by first-class mail, return receipt
requested, and shall be deemed given (i) when made, if made by hand delivery,
(ii) upon confirmation, if made by telecopier, (iii) one (1) Business Day after
being deposited with such courier, if made by overnight courier or (iv) on the
date indicated on the notice of receipt, if made by first-class mail, to the
parties as follows:

          (w)   if to a Holder of Registrable Securities that is not a Notice
     Holder, at the address for such Holder then appearing in the Registrar (as
     defined in the Indenture);

          (x)   if to a Notice Holder, at the most current address given by such
     Holder to the Company in a Notice and Questionnaire or any amendment
     thereto;

          (y)   if to the Company, to:

          OSI Pharmaceuticals, Inc.
          58 South Service Road, Suite 110
          Melville, NY 11747
          Attention: Barbara Wood, General Counsel

          Telephone No.: (631) 962-2000
          Telecopy No.: (631) 752-3880

          and

          (z)   if to the Initial Purchasers, to:

          Merrill Lynch & Co., Merrill Lynch, Pierce, Fenner & Smith
          Incorporated

                                       17
<Page>

          World Financial Center
          North Tower
          250 Vesey Street
          New York, New York 10080
          Attention: Syndicate Department

          Telecopy No.: (212) 449-1000

or to such other address as such person may have furnished to the other persons
identified in this Section 8(c) in writing in accordance herewith.

          (d)   APPROVAL OF HOLDERS. Whenever the consent or approval of Holders
of a specified percentage of Registrable Securities is required hereunder, the
Registrable Securities held by the Company or its affiliates (as such term is
defined in Rule 405 under the Securities Act) (other than the Initial Purchasers
or subsequent Holders of Registrable Securities if such subsequent Holders are
deemed to be such affiliates solely by reason of their holdings of such
Registrable Securities) shall not be counted in determining whether such consent
or approval was given by the Holders of such required percentage.

          (e)   SUCCESSORS AND ASSIGNS. Any person who purchases any Registrable
Securities from an Initial Purchaser shall be deemed, for purposes of this
Agreement, to be an assignee of such Initial Purchaser. This Agreement shall
inure to the benefit of and be binding upon the successors and assigns of each
of the parties and shall inure to the benefit of and be binding upon each Holder
of any Registrable Securities.

          (f)   COUNTERPARTS. This Agreement may be executed in any number of
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be original and all of which taken together
shall constitute one and the same agreement.

          (g)   HEADINGS. The headings in this Agreement are for convenience of
reference only and shall not limit or otherwise affect the meaning hereof.

          (h)   GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED
IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO
CONFLICTS OF LAWS PRINCIPLES THEREOF.

          (i)   SEVERABILITY. If any term, provision, covenant or restriction of
this Agreement is held to be invalid, illegal, void or unenforceable, the
remainder of the terms, provisions, covenants and restrictions set forth herein
shall remain in full force and effect and shall in no way be affected, impaired
or invalidated thereby, and the parties hereto shall use their best efforts to
find and employ an alternative means to achieve the same or substantially the
same result as that contemplated by such term, provision, covenant or
restriction, it being intended that all of the rights and privileges of the
parties shall be enforceable to the fullest extent permitted by law.

                                       18
<Page>

          (j)   ENTIRE AGREEMENT. This Agreement is intended by the parties as a
final expression of their agreement and is intended to be a complete and
exclusive statement of the agreement and understanding of the parties hereto in
respect of the subject matter contained herein and the registration rights
granted by the Company with respect to the Registrable Securities. Except as
provided in the Purchase Agreement, there are no restrictions, promises,
warranties or undertakings, other than those set forth or referred to herein,
with respect to the registration rights granted by the Company with respect to
the Registrable Securities. This Agreement supersedes all prior agreements and
undertakings among the parties with respect to such registration rights.

          (k)   TERMINATION. This Agreement and the obligations of the parties
hereunder shall terminate upon the expiration of the Effectiveness Period,
except for any liabilities or obligations under Sections 4, 5 or 6 hereof and
the obligations to make payments of and provide for liquidated damages under
Section 2(e) hereof to the extent such damages accrue prior to the end of the
Effectiveness Period, each of which shall remain in effect in accordance with
its terms.

                [Remainder of this page intentionally left blank]

                                       19
<Page>

          IN WITNESS WHEREOF, the parties have executed this Registration Rights
Agreement as of the date first written above.

                                              OSI PHARMACEUTICALS, INC.

                                              By: /s/ ROBERT L. VAN NOSTRAND
                                                  ------------------------------
                                              Name:   Robert L. Van Nostrand
                                              Title:  Vice President and
                                                      Chief Financial Officer

Confirmed and accepted as
of the date first above written:

MERRILL LYNCH & CO.
MERRILL LYNCH, PIERCE, FENNER & SMITH
     INCORPORATED
ROBERTSON STEPHENS, INC.
ADAMS, HARKNESS & HILL, INC.
LAZARD FRERES & CO. LLC

MERRILL LYNCH, PIERCE, FENNER & SMITH
     INCORPORATED

By: /s/ ANTHONY GIBNEY
    -----------------------
        Authorized Signatory

                                       20<Page>

                                                                    EXHIBIT 4.5

                                                                  EXECUTION COPY

                            ACCOUNT CONTROL AGREEMENT

          ACCOUNT CONTROL AGREEMENT (this "AGREEMENT") dated as of February 1,
2002, among OSI Pharmaceuticals, Inc., a Delaware corporation (the "PLEDGOR"),
The Bank of New York, a New York banking corporation, as Trustee (the "SECURED
PARTY"), and The Bank of New York, a New York banking corporation, as securities
intermediary and depository bank (the "ACCOUNT HOLDER").

PRELIMINARY STATEMENTS:

          (1)   The Pledgor has granted the Secured Party a security interest
(the "SECURITY INTEREST") in certain security entitlements (the "PLEDGED
SECURITY ENTITLEMENTS") with respect to certain U.S. Treasury securities (the
"PLEDGED FINANCIAL ASSETS") identified on Schedule I attached hereto maintained
by the Pledgor with the Account Holder and carried from time to time in an
account with the Account Holder, ABA No. 021000018, Account No. 341431 at its
office at 101 Barclay Street, New York, New York 10286, in the name of "OSI
Pharmaceuticals Pledge Account" (the "ACCOUNT") and all additions thereto and
substitutions and proceeds thereof, pursuant to, and as more particularly
described in, a Collateral Pledge and Security Agreement dated as of February 1,
2002, among the Pledgor and the Trustee (as the same may hereafter be amended,
supplemented or otherwise modified from time to time, the "PLEDGE AGREEMENT";
terms defined in the Pledge Agreement and not otherwise defined herein being
used herein as therein defined). The Pledgor acknowledges having received value
for such pledge.

          (2)   Terms defined in Article 8 or 9 of the Uniform Commercial Code
in effect in the State of New York ("N.Y. UNIFORM COMMERCIAL CODE") are used in
this Agreement as such terms are defined in such Article 8 or 9.

          (3)   The Pledgor, the Trustee and the Account Holder are delivering
this Agreement pursuant to the terms of Section 4(f) of the Pledge Agreement.

          NOW, THEREFORE, in consideration of the premises and of the mutual
agreements contained herein, the parties hereto hereby agree as follows:

          SECTION 1. THE ACCOUNTS. The Account Holder represents and warrants
to, and agrees with, the Secured Party that:

          (a)   The Account Holder maintains the Account for the Pledgor, and
     all the Pledged Financial Assets and all additions thereto and
     substitutions and proceeds thereof held by the Account Holder for the
     account of the Pledgor are, and will continue to be, credited to the
     Account.

<Page>

          (b)   To the extent that funds are credited to the Account, the
     Account is a deposit account; and to the extent that financial assets are
     credited to the Account, the Account is a securities account. The Account
     Holder is (i) the bank with which the Account is maintained and (ii) the
     securities intermediary with respect to financial assets held in the
     Account. The Pledgor is (x) the Account Holder's customer with respect to
     the Account and (y) the entitlement holder with respect to financial assets
     credited from time to time to the Account.

          (c)   Notwithstanding any other agreement to the contrary, the Account
     Holder's jurisdiction with respect to the Account for purposes of the N.Y.
     Uniform Commercial Code is, and will continue to be for so long as the
     Security Interest shall be in effect, the State of New York.

          (d)   Attached as Exhibit A hereto is the statement of the Account as
     of the date hereof showing the property credited to the Account.

          (e)   The Account Holder does not know of any claim to or interest in
     the Account or any property (including, without limitation, funds and
     financial assets) credited to the Account, except for claims and interests
     of the parties referred to in this Agreement.

          SECTION 2. CONTROL BY SECURED PARTY. The Account Holder will comply
with (i) all instructions directing disposition of the funds in the Account,
(ii) all notifications and entitlement orders that the Account Holder receives
directing it to transfer or redeem any financial asset in the Account, and (iii)
all other directions concerning the Account, including, without limitation,
directions to distribute to the Secured Party proceeds of any such transfer or
redemption or interest or dividends on property in the Account (any such
instruction, notification or direction referred to in clause (i), (ii) or (iii)
above being an "ACCOUNT DIRECTION"), in each case of clauses (i), (ii) and (iii)
above originated by the Secured Party without further consent by the Pledgor or
any other Person. The Account Holder will comply with Account Directions and
other directions concerning the Account originated by, and only by, the Secured
Party. The Account Holder acknowledges that the Secured Party has exclusive
control over the Account and all Pledged Financial Assets contained therein from
time to time.

          SECTION 3. PRIORITY OF SECURED PARTY'S SECURITY INTEREST.

          (a)   The Account Holder (i) subordinates to the Security Interest and
     in favor of the Secured Party any security interest, lien, or right of
     recoupment or setoff that the Account Holder may have, now or in the
     future, against the Account or any property (including, without limitation,
     any funds and financial assets) credited to the Account, and (ii) agrees
     that it will not exercise any right in respect of any such security
     interest or lien or any such right of recoupment or setoff until the
     Security Interest is terminated, EXCEPT that the Account Holder (A) will
     retain its prior security interest and lien on property credited to
     the Account, (B) may exercise any right in respect of such security
     interest or lien, and (C) may exercise any right of recoupment or setoff
     against the Account, in the case of clauses (A), (B) and (C) above, to
     secure or to satisfy, and only to secure or to satisfy, payment (x) for
     such property, (y) for its customary fees and

                                        2
<Page>

     expenses for the routine maintenance and operation of the Account, and (z)
     if the Account is a deposit account, for the face amount of any items that
     have been credited to the Account but are subsequently returned unpaid
     because of uncollected or insufficient funds.

          (b)   The Account Holder will not enter into any other agreement with
     any Person relating to Account Directions or other directions with respect
     to the Account.

          SECTION 4. STATEMENTS, CONFIRMATIONS, AND NOTICES OF ADVERSE CLAIMS.

          (a)   The Account Holder will send copies of all statements and
     confirmations for the Account simultaneously to the Secured Party and the
     Pledgor.

          (b)   When the Account Holder knows of any claim or interest in the
     Account or any property (including, without limitation, funds and financial
     assets) credited to the Account other than the claims and interests of the
     parties referred to in this Agreement, the Account Holder will promptly
     notify the Secured Party and the Pledgor of such claim or interest.

          SECTION 5. THE ACCOUNT HOLDER'S RESPONSIBILITY.

          (a)   The Account Holder will be liable to the Secured Party for
     complying with Account Directions or other directions concerning the
     Account from the Pledgor or any Person other than the Secured Party.

          (b)   The Account Holder will not be liable to the Pledgor or the
     Secured Party for complying with an Account Direction or other direction
     concerning the Account originated by the Secured Party, even if the Pledgor
     notifies the Account Holder that the Secured Party is not legally entitled
     to issue the Account Direction or such other direction unless the Account
     Holder takes the action after it is served with an injunction, restraining
     order, or other legal process enjoining it from doing so, issued by a court
     of competent jurisdiction, and had a reasonable opportunity to act on the
     injunction, restraining order or other legal process.

          (c)   This Agreement does not create any obligation of the Account
     Holder except for those expressly set forth in this Agreement and, to the
     extent that the Account is a securities account, in Part 5 of Article 8 of
     the N.Y. Uniform Commercial Code and, to the extent that the Account is a
     deposit account, in Article 4 of the N.Y. Uniform Commercial Code. In
     particular, the Account Holder need not investigate whether the Secured
     Party is entitled under the Secured Party's agreements with the Pledgor to
     give an Account Direction or other direction concerning the Account. The
     Account Holder may rely on notices and communications it believes given by
     the appropriate party.

          SECTION 6. INDEMNITY. The Pledgor will indemnify the Account Holder,
its officers, directors, employees and agents against claims, liabilities and
expenses arising out of this Agreement (including, without limitation,
reasonable attorney's fees and disbursements), except to the extent the claims,
liabilities or expenses are caused by the Account Holder's gross

                                        3
<Page>

negligence or willful misconduct as found by a court of competent jurisdiction
in a final, non-appealable judgment.

          SECTION 7. TERMINATION; SURVIVAL.

          (a)   This Agreement shall terminate automatically upon receipt by the
     Account Holder of written notice executed by two officers of the Trustee
     that all of the Secured Obligations have been paid in full in cash or
     otherwise satisfied or all of the Collateral has been released, which ever
     is earlier, and the Account Holder shall thereafter be relieved of all
     duties and obligations hereunder.

          (b)   The Account Holder may terminate this Agreement on 60 days'
     prior notice to the Secured Party and the Pledgor, PROVIDED that before
     such termination the Account Holder and the Pledgor shall make arrangements
     to transfer the property (including, without limitation, all funds and
     financial assets) credited to the Account to another Account Holder that
     shall have executed, together with the Pledgor, a control agreement in
     favor of the Secured Party in respect of such property in substantially the
     form of this Agreement or otherwise in form and substance satisfactory to
     the Secured Party.

          (c)   Sections 5 and 6 will survive termination of this Agreement.

          SECTION 8. GOVERNING LAW. This Agreement and the Account will be
governed by the law of the State of New York. The Account Holder and the Pledgor
may not change the law governing the Account without the Secured Party's express
prior written agreement.

          SECTION 9. ENTIRE AGREEMENT. This Agreement is the entire agreement,
and supersedes any prior agreements, and contemporaneous oral agreements, of the
parties concerning its subject matter.

          SECTION 10. AMENDMENTS. No amendment of, or waiver of a right under,
this Agreement will be binding unless it is in writing and signed by the party
to be charged.

          SECTION 11. FINANCIAL ASSETS. The Account Holder agrees with the
Secured Party and the Pledgor that, to the fullest extent permitted by
applicable law, all property (other than funds) credited from time to time to
the Account will be treated as financial assets under Article 8 of the N.Y.
Uniform Commercial Code.

          SECTION 12. NOTICES. A notice or other communication to a party under
this Agreement will be in writing (except that Account Directions may be given
orally), will be sent to the party's address set forth under its name below or
to such other address as the party may notify the other parties and will be
effective on receipt.

          SECTION 13. BINDING EFFECT. This Agreement shall become effective when
it shall have been executed by the Pledgor, the Secured Party and the Account
Holder, and thereafter shall be binding upon and inure to the benefit of the
Pledgor, the Secured Party and the Account Holder and their respective
successors and assigns.

                                        4
<Page>

          SECTION 14. EXECUTION IN COUNTERPARTS. This Agreement may be executed
in any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed shall be deemed to be an original
and all of which taken together shall constitute one and the same agreement.
Delivery of an executed counterpart of a signature page to this Agreement by
telecopier shall be effective as delivery of an original executed counterpart of
this Agreement.

                                        5
<Page>

          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed by their respective officers thereunto duly authorized, as of the
date first above written.

                                       OSI PHARMACEUTICALS, INC.

                                       By /s/ ROBERT L. VAN NOSTRAND
                                          --------------------------
                                          Name:    Robert L. Van Nostrand
                                          Title:   Vice President and
                                                   Chief Financial Officer

                                       Address:
                                       58 South Service Road
                                       Melville, NY 11747

                                       THE BANK OF NEW YORK, as Trustee

                                       By /s/ JULIE SALOVITCH-MILLER
                                          --------------------------
                                          Name:    Julie Salovitch-Miller
                                          Title:   Vice President

                                       Address:
                                       5 Penn Plaza, 13th Floor
                                       New York, NY 10001

                                       THE BANK OF NEW YORK

                                       By /s/ GEOVANNI BARRIS
                                          Name:    Geovanni Barris
                                          Title:   Vice President

                                       Address:
                                       5 Penn Plaza, 13th Floor
                                       New York, NY 10001

                                        6
<Page>

                                    EXHIBIT A

<Table>
<Caption>
                                                                   FACE AMOUNT
DESCRIPTION OF ASSET                          CUSIP NUMBER         OF ASSET
--------------------                          ------------         -----------
<S>                                             <C>                <C>
US TREASURY BILLS                               912795KU4          USD 4,000,000
US TREAS NTS SEC STRIPPED                       912833FR6          USD 4,000,000
US TREAS NTS SEC STRIPPED                       912833FS4          USD 4,000,000
UNITED STATES TREAS NT STRIPPED PRIN PMT        912820DJ3          USD 4,000,000
UNITED STATES TREAS NT STRP PRIN PMT            912820BJ5          USD 4,000,000
US TREASURY BD STRIPPED                         912803AB9          USD 4,000,000
</Table>

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