<PAGE>

                                                                    EXHIBIT 4.11

                           ONYX PHARMACEUTICALS, INC.

                                       AND

                               , AS WARRANT AGENT

                             FORM OF PREFERRED STOCK
                                WARRANT AGREEMENT

                                   DATED AS OF

                         -------------------------------

                           ONYX PHARMACEUTICALS, INC.
                    FORM OF PREFERRED STOCK WARRANT AGREEMENT

      PREFERRED STOCK WARRANT AGREEMENT, dated as of ______________ between ONYX
PHARMACEUTICALS, INC., a Delaware corporation (the "COMPANY") and
________________, a [corporation] [national banking association] organized and
existing under the laws of ________________ and having a corporate trust office
in ___________________, as warrant agent (the "WARRANT AGENT").

      WHEREAS, the Company proposes to sell [if Warrants are sold with other
securities -- [title of such other securities being offered] (the "OTHER
SECURITIES") with] warrant certificates evidencing one or more warrants (the
"WARRANTS" or, individually, a "WARRANT") representing the right to purchase
[title of Preferred Stock purchasable through exercise of Warrants] (the
"WARRANT SECURITIES"), such warrant certificates and other warrant certificates
issued pursuant to this Agreement being herein called the "WARRANT
CERTIFICATES"; and

      WHEREAS, the Company desires the Warrant Agent to act on behalf of the
Company, and the Warrant Agent is willing so to act, in connection with the
issuance, registration, transfer, exchange, exercise and replacement of the
Warrant Certificates, and in this Agreement wishes to set forth, among other
things, the form and provisions of the Warrant Certificates and the terms and
conditions on which they may be issued, registered, transferred, exchanged,
exercised and replaced;

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

                                       1.
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                                   ARTICLE 1

    ISSUANCE OF WARRANTS AND EXECUTION AND DELIVERY OF WARRANT CERTIFICATES

      1.1 ISSUANCE OF WARRANTS. [If Warrants alone--Upon issuance, each
Warrant Certificate shall evidence one or more Warrants.] [If Other Securities
and Warrants--Warrants shall be [initially] issued in connection with the
issuance of the Other Securities [but shall be separately transferable on and
after _______________ (the "DETACHABLE DATE")] [and shall not be separately
transferable] and each Warrant Certificate shall evidence one or more Warrants.]
Each Warrant evidenced thereby shall represent the right, subject to the
provisions contained herein and therein, to purchase one Warrant Security. [If
Other Securities and Warrants--Warrant Certificates shall be initially issued
in units with the Other Securities and each Warrant Certificate included in such
a unit shall evidence __________ Warrants for each [$_________ principal amount]
[ __________ shares] of Other Securities included in such unit.]

      1.2 EXECUTION AND DELIVERY OF WARRANT CERTIFICATES. Each Warrant
Certificate, whenever issued, shall be in registered form substantially in the
form set forth in Exhibit A hereto, shall be dated the date of its
countersignature by the Warrant Agent and may have such letters, numbers, or
other marks of identification or designation and such legends or endorsements
printed, lithographed or engraved thereon as the officers of the Company
executing the same may approve (execution thereof to be conclusive evidence of
such approval) and as are not inconsistent with the provisions of this
Agreement, or as may be required to comply with any law or with any rule or
regulation made pursuant thereto or with any rule or regulation of any
securities exchange on which the Warrants may be listed, or to conform to usage.
The Warrant Certificates shall be signed on behalf of the Company by any of its
present or future chief executive officers, presidents, senior vice presidents,
vice presidents, chief financial officers, chief legal officers, treasurers,
assistant treasurers, controllers, assistant controllers, secretaries or
assistant secretaries under its corporate seal reproduced thereon. Such
signatures may be manual or facsimile signatures of such authorized officers and
may be imprinted or otherwise reproduced on the Warrant Certificates. The seal
of the Company may be in the form of a facsimile thereof and may be impressed,
affixed, imprinted or otherwise reproduced on the Warrant Certificates.

      No Warrant Certificate shall be valid for any purpose, and no Warrant
evidenced thereby shall be exercisable, until such Warrant Certificate has been
countersigned by the manual signature of the Warrant Agent. Such signature by
the Warrant Agent upon any Warrant Certificate executed by the Company shall be
conclusive evidence that the Warrant Certificate so countersigned has been duly
issued hereunder.

      In case any officer of the Company who shall have signed any of the
Warrant Certificates either manually or by facsimile signature shall cease to be
such officer before the Warrant Certificates so signed shall have been
countersigned and delivered by the Warrant Agent, such Warrant Certificates may
be countersigned and delivered notwithstanding that the person who signed
Warrant Certificates ceased to be such officer of the Company; and any Warrant
Certificate may be signed on behalf of the Company by such persons as, at the
actual date of the

                                       2.
<PAGE>

execution of such Warrant Certificate, shall be the proper officers of the
Company, although at the date of the execution of this Agreement any such person
was not such officer.

      The term "holder" or "holder of a Warrant Certificate" as used herein
shall mean any person in whose name at the time any Warrant Certificate shall be
registered upon the books to be maintained by the Warrant Agent for that purpose
[If Other Securities and Warrants are not immediately detachable--or upon the
registration of the Other Securities prior to the Detachable Date. Prior to the
Detachable Date, the Company will, or will cause the registrar of the Other
Securities to, make available at all times to the Warrant Agent such information
as to holders of the Other Securities as may be necessary to keep the Warrant
Agent's records up to date].

      1.3 ISSUANCE OF WARRANT CERTIFICATES. Warrant Certificates evidencing the
right to purchase Warrant Securities may be executed by the Company and
delivered to the Warrant Agent upon the execution of this Warrant Agreement or
from time to time thereafter. The Warrant Agent shall, upon receipt of Warrant
Certificates duly executed on behalf of the Company, countersign such Warrant
Certificates and shall deliver such Warrant Certificates to or upon the order of
the Company.

                                   ARTICLE 2

                WARRANT PRICE, DURATION AND EXERCISE OF WARRANTS

      2.1 WARRANT PRICE. During the period specified in Section 2.2, each
Warrant shall, subject to the terms of this Warrant Agreement and the applicable
Warrant Certificate, entitle the holder thereof to purchase the number of
Warrant Securities specified in the applicable Warrant Certificate at an
exercise price of $      per Warrant Security, subject to adjustment upon the
occurrence of certain events, as hereinafter provided. Such purchase price per
Warrant Security is referred to in this Agreement as the "WARRANT PRICE."

      2.2 DURATION OF WARRANTS. Each Warrant may be exercised in whole or in
part at any time, as specified herein, on or after [the date thereof] [________]
and at or before ______ p.m., [City] time, on ______________ or such later date
as the Company may designate by notice to the Warrant Agent and the holders of
Warrant Certificates mailed to their addresses as set forth in the record books
of the Warrant Agent (the "EXPIRATION DATE"). Each Warrant not exercised at or
before _________ p.m., [City] time, on the Expiration Date shall become void,
and all rights of the holder of the Warrant Certificate evidencing such Warrant
under this Agreement shall cease.

      2.3 EXERCISE OF WARRANTS.

            (a) During the period specified in Section 2.2, the Warrants may be
exercised to purchase a whole number of Warrant Securities in registered form by
providing certain information as set forth on the reverse side of the Warrant
Certificate and by paying in full, in lawful money of the United States of
America, [in cash or by certified check or official bank check in New York
Clearing House funds] [by bank wire transfer in immediately available funds] the
Warrant Price for each Warrant Security with respect to which a Warrant is being
exercised to the Warrant Agent at its corporate trust office, provided that such
exercise is subject

                                       3.
<PAGE>

to receipt within five business days of such payment by the Warrant Agent of the
Warrant Certificate with the form of election to purchase Warrant Securities set
forth on the reverse side of the Warrant Certificate properly completed and duly
executed. The date on which payment in full of the Warrant Price is received by
the Warrant Agent shall, subject to receipt of the Warrant Certificate as
aforesaid, be deemed to be the date on which the Warrant is exercised; provided,
however, that if, at the date of receipt of such Warrant Certificates and
payment in full of the Warrant Price, the transfer books for the Warrant
Securities purchasable upon the exercise of such Warrants shall be closed, no
such receipt of such Warrant Certificates and no such payment of such Warrant
Price shall be effective to constitute the person so designated to be named as
the holder of record of such Warrant Securities on such date, but shall be
effective to constitute such person as the holder of record of such Warrant
Securities for all purposes at the opening of business on the next succeeding
day on which the transfer books for the Warrant Securities purchasable upon the
exercise of such Warrants shall be opened, and the certificates for the Warrant
Securities in respect of which such Warrants are then exercised shall be
issuable as of the date on such next succeeding day on which the transfer books
shall next be opened, and until such date the Company shall be under no duty to
deliver any certificate for such Warrant Securities. The Warrant Agent shall
deposit all funds received by it in payment of the Warrant Price in an account
of the Company maintained with it and shall advise the Company by telephone at
the end of each day on which a payment for the exercise of Warrants is received
of the amount so deposited to its account. The Warrant Agent shall promptly
confirm such telephone advice to the Company in writing.

            (b) The Warrant Agent shall, from time to time, as promptly as
practicable, advise the Company of (i) the number of Warrant Securities with
respect to which Warrants were exercised, (ii) the instructions of each holder
of the Warrant Certificates evidencing such Warrants with respect to delivery of
the Warrant Securities to which such holder is entitled upon such exercise,
(iii) delivery of Warrant Certificates evidencing the balance, if any, of the
Warrants for the remaining Warrant Securities after such exercise, and (iv) such
other information as the Company shall reasonably require.

            (c) As soon as practicable after the exercise of any Warrant, the
Company shall issue to or upon the order of the holder of the Warrant
Certificate evidencing such Warrant the Warrant Securities to which such holder
is entitled, in fully registered form, registered in such name or names as may
be directed by such holder. If fewer than all of the Warrants evidenced by such
Warrant Certificate are exercised, the Company shall execute, and an authorized
officer of the Warrant Agent shall manually countersign and deliver, a new
Warrant Certificate evidencing Warrants for the number of Warrant Securities
remaining unexercised.

            (d) The Company shall not be required to pay any stamp or other tax
or other governmental charge required to be paid in connection with any transfer
involved in the issue of the Warrant Securities, and in the event that any such
transfer is involved, the Company shall not be required to issue or deliver any
Warrant Security until such tax or other charge shall have been paid or it has
been established to the Company's satisfaction that no such tax or other charge
is due.

            (e) Prior to the issuance of any Warrants there shall have been
reserved, and the Company shall at all times through the Expiration Date keep
reserved, out of its authorized

                                       4.
<PAGE>

but unissued Warrant Securities, a number of shares sufficient to provide for
the exercise of the Warrants.

                                   ARTICLE 3

     OTHER PROVISIONS RELATING TO RIGHTS OF HOLDERS OF WARRANT CERTIFICATES

      3.1 NO RIGHTS AS WARRANT SECURITYHOLDER CONFERRED BY WARRANTS OR WARRANT
CERTIFICATES. No Warrant Certificate or Warrant evidenced thereby shall entitle
the holder thereof to any of the rights of a holder of Warrant Securities,
including, without limitation, the right to receive the payment of dividends or
distributions, if any, on the Warrant Securities or to exercise any voting
rights, except to the extent expressly set forth in this Agreement or the
applicable Warrant Certificate.

      3.2 LOST, STOLEN, MUTILATED OR DESTROYED WARRANT CERTIFICATES. Upon
receipt by the Warrant Agent of evidence reasonably satisfactory to it and the
Company of the ownership of and the loss, theft, destruction or mutilation of
any Warrant Certificate and/or indemnity reasonably satisfactory to the Warrant
Agent and the Company and, in the case of mutilation, upon surrender of the
mutilated Warrant Certificate to the Warrant Agent for cancellation, then, in
the absence of notice to the Company or the Warrant Agent that such Warrant
Certificate has been acquired by a bona fide purchaser, the Company shall
execute, and an authorized officer of the Warrant Agent shall manually
countersign and deliver, in exchange for or in lieu of the lost, stolen,
destroyed or mutilated Warrant Certificate, a new Warrant Certificate of the
same tenor and evidencing Warrants for a like number of Warrant Securities. Upon
the issuance of any new Warrant Certificate under this Section 3.2, the Company
may require the payment of a sum sufficient to cover any tax or other
governmental charge that may be imposed in relation thereto and any other
expenses (including the fees and expenses of the Warrant Agent) in connection
therewith. Every substitute Warrant Certificate executed and delivered pursuant
to this Section 3.2 in lieu of any lost, stolen or destroyed Warrant Certificate
shall represent an additional contractual obligation of the Company, whether or
not the lost, stolen or destroyed Warrant Certificate shall be at any time
enforceable by anyone, and shall be entitled to the benefits of this Agreement
equally and proportionately with any and all other Warrant Certificates duly
executed and delivered hereunder. The provisions of this Section 3.2 are
exclusive and shall preclude (to the extent lawful) all other rights and
remedies with respect to the replacement of mutilated, lost, stolen or destroyed
Warrant Certificates.

      3.3 HOLDER OF WARRANT CERTIFICATE MAY ENFORCE RIGHTS. Notwithstanding any
of the provisions of this Agreement, any holder of a Warrant Certificate,
without the consent of the Warrant Agent, the holder of any Warrant Securities
or the holder of any other Warrant Certificate, may, in such holder's own behalf
and for such holder's own benefit, enforce, and may institute and maintain any
suit, action or proceeding against the Company suitable to enforce, or otherwise
in respect of, such holder's right to exercise the Warrants evidenced by such
holder's Warrant Certificate in the manner provided in such holder's Warrant
Certificate and in this Agreement.

                                       5.
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      3.4 ADJUSTMENTS.

            (a) In case the Company shall at any time subdivide its outstanding
shares of [title of Preferred Stock purchasable through exercise of Warrants]
into a greater number of shares, the Warrant Price in effect immediately prior
to such subdivision shall be proportionately reduced and the number of Warrant
Securities purchasable under the Warrants shall be proportionately increased.
Conversely, in case the outstanding shares of [title of Preferred Stock
purchasable through exercise of Warrants] of the Company shall be combined into
a smaller number of shares, the Warrant Price in effect immediately prior to
such combination shall be proportionately increased and the number of Warrant
Securities purchasable under the Warrants shall be proportionately decreased.

            (b) If at any time or from time to time the holders of [title of
Preferred Stock purchasable through exercise of Warrants] (or any shares of
stock or other securities at the time receivable upon the exercise of the
Warrants) shall have received or become entitled to receive, without payment
therefore,

                  (i) [title of Preferred Stock purchasable through exercise of
Warrants] or any shares of stock or other securities which are at any time
directly or indirectly convertible into or exchangeable for [title of Preferred
Stock purchasable through exercise of Warrants], or any rights or options to
subscribe for, purchase or otherwise acquire any of the foregoing by way of
dividend or other distribution;

                  (ii) any cash paid or payable otherwise than in accordance
with the terms of [title of Preferred Stock purchasable through exercise of
Warrants] or otherwise than as a cash dividend paid or payable out of the
Company's current or retained earnings;

                  (iii) any evidence of the Company's indebtedness or rights to
subscribe for or purchase the Company's indebtedness; or

                  (iv) [title of Preferred Stock purchasable through exercise of
Warrants] or additional stock or other securities or property (including cash)
by way of spinoff, split-up, reclassification, combination of shares or similar
corporate rearrangement (other than shares of [title of Preferred Stock
purchasable through exercise of Warrants] issued as a stock split or adjustments
in respect of which shall be covered by the terms of Section 3.4(a) above), then
and in each such case, the holder of each Warrant shall, upon the exercise of
the Warrant, be entitled to receive, in addition to the number of Warrant
Securities receivable thereupon, and without payment of any additional
consideration therefore, the amount of stock and other securities and property
(including cash and indebtedness (or rights to subscribe for or purchase
indebtedness) which such holder would hold on the date of such exercise had he
been the holder of record of such Warrant Securities as of the date on which
holders of [title of Preferred Stock purchasable through exercise of Warrants]
received or became entitled to receive such shares or all other additional stock
and other securities and property.

            (c) In case of (i) any reclassification, capital reorganization, or
change in the [title of Preferred Stock purchasable through the exercise of the
Warrants] of the Company (other than as a result of a subdivision, combination
or stock dividend provided for in Section 3.4(a) or

                                       6.
<PAGE>

Section 3.4(b) above), (ii) share exchange, merger or similar transaction of the
Company with or into another person or entity (other than a share exchange,
merger or similar transaction in which the Company is the acquiring or surviving
corporation and which does not result in any change in the [title of Preferred
Stock purchasable through the exercise of the Warrants] other than the issuance
of additional shares of [title of Preferred Stock purchasable through the
exercise of the Warrants]) or (iii) the sale, exchange, lease, transfer or other
disposition of all or substantially all of the properties and assets of the
Company as an entirety (in any such case, a "REORGANIZATION EVENT"), then, as a
condition of such Reorganization Event, lawful provisions shall be made, and
duly executed documents evidencing the same from the Company or its successor
shall be delivered to the holders of the Warrants, so that the holders of the
Warrants shall have the right at any time prior to the expiration of the
Warrants to purchase, at a total price equal to that payable upon the exercise
of the Warrants, the kind and amount of shares of stock and other securities and
property receivable in connection with such Reorganization Event by a holder of
the same number of shares of [title of Preferred Stock purchasable through the
exercise of the Warrants] as were purchasable by the holders of the Warrants
immediately prior to such Reorganization Event. In any such case appropriate
provisions shall be made with respect to the rights and interests of the holders
of the Warrants so that the provisions hereof shall thereafter be applicable
with respect to any shares of stock or other securities and property deliverable
upon exercise the Warrants, and appropriate adjustments shall be made to the
Warrant Price payable hereunder provided the aggregate purchase price shall
remain the same. In the case of any transaction described in clauses (ii) and
(iii) above, the Company shall thereupon be relieved of any further obligation
hereunder or under the Warrants, and the Company as the predecessor corporation
may thereupon or at any time thereafter be dissolved, wound up or liquidated.
Such successor or assuming entity thereupon may cause to be signed, and may
issue either in its own name or in the name of the Company, any or all of the
Warrants issuable hereunder which heretofore shall not have been signed by the
Company, and may execute and deliver securities in its own name, in fulfillment
of its obligations to deliver Warrant Securities upon exercise of the Warrants.
All the Warrants so issued shall in all respects have the same legal rank and
benefit under this Agreement as the Warrants theretofore or thereafter issued in
accordance with the terms of this Agreement as though all of such Warrants had
been issued at the date of the execution hereof. In any case of any such
Reorganization Event, such changes in phraseology and form (but not in
substance) may be made in the Warrants thereafter to be issued as may be
appropriate.

      The Warrant Agent may receive a written opinion of legal counsel as
conclusive evidence that any such Reorganization Event complies with the
provisions of this Section 3.4.

            (d) The Company may, at its option, at any time until the Expiration
Date, reduce the then current Warrant Price to any amount deemed appropriate by
the Board of Directors of the Company for any period not exceeding twenty
consecutive days (as evidenced in a resolution adopted by such Board of
Directors), but only upon giving the notices required by Section 3.5 at least
ten days prior to taking such action.

            (e) Except as herein otherwise expressly provided, no adjustment in
the Warrant Price shall be made by reason of the issuance of any securities of
the Company or for any other reason whatsoever.

                                       7.
<PAGE>

            (f) No fractional Warrant Securities shall be issued upon the
exercise of Warrants. If more than one Warrant shall be exercised at one time by
the same holder, the number of full Warrant Securities which shall be issuable
upon such exercise shall be computed on the basis of the aggregate number of
Warrant Securities purchased pursuant to the Warrants so exercised. Instead of
any fractional Warrant Security which would otherwise be issuable upon exercise
of any Warrant, the Company shall pay a cash adjustment in respect of such
fraction in an amount equal to the same fraction of the last sales price (or bid
price if there were no sales) per Warrant Security, in either case as reported
on the New York Stock Exchange Composite Tape on the business day which next
precedes the day of exercise or, if the Warrant Securities are not then listed
or admitted to trading on the New York Stock Exchange, on the principal national
securities exchange on which the Warrant Securities are listed or admitted to
trading or, if not listed or admitted to trading on any national securities
exchange, on the National Market System of the National Association of
Securities Dealers, Inc. Automated Quotations System ("NASDAQ"), or if the
Warrant Securities are not then listed or admitted to trading on any national
securities exchange or quoted on the National Market System of NASDAQ, the
average of the closing high bid and low asked prices in the over-the-counter
market, as reported by NASDAQ, or such other system then in use, or if on any
such date the Warrant Securities are not quoted by any such organization, an
amount equal to the same fraction of the average of the closing bid and asked
prices as furnished by any New York Stock Exchange firm selected from time to
time by the Company for that purpose at the close of business on the business
day which next precedes the day of exercise.

            (g) Whenever the Warrant Price then in effect is adjusted as herein
provided, the Company shall mail to each holder of the Warrants at such holder's
address as it shall appear on the books of the Company a statement setting forth
the adjusted Warrant Price then and thereafter effective under the provisions
hereof, together with the facts, in reasonable detail, upon which such
adjustment is based.

      3.5 NOTICE TO WARRANTHOLDERS. In case the Company shall (a) effect any
dividend or distribution described in Section 3.4(b), (b) effect any
Reorganization Event, (c) make any distribution on or in respect of the [title
of Preferred Stock purchasable through the exercise of the Warrants] in
connection with the dissolution, liquidation or winding up of the Company, or
(d) reduce the then current Warrant Price pursuant to Section 3.4(d), then the
Company shall mail to each holder of Warrants at such holder's address as it
shall appear on the books of the Warrant Agent, at least ten days prior to the
applicable date hereinafter specified, a notice stating (x) the record date for
such dividend or distribution, or, if a record is not to be taken, the date as
of which the holders of record of [title of Preferred Stock purchasable through
the exercise of Warrants] that will be entitled to such dividend or distribution
are to be determined, (y) the date on which such Reorganization Event,
dissolution, liquidation or winding up is expected to become effective, and the
date as of which it is expected that holders of [title of Preferred Stock
purchasable through the exercise of the Warrants] of record shall be entitled to
exchange their shares of [title of Preferred Stock purchasable through the
exercise of the Warrants] for securities or other property deliverable upon such
Reorganization Event, dissolution, liquidation or winding up, or (z) the first
date on which the then current Warrant Price shall be reduced pursuant to
Section 3.4(d). No failure to mail such notice nor any defect therein or in the
mailing thereof shall affect any such transaction or any adjustment in the
Warrant Price required by Section 3.4.

                                       8.
<PAGE>

      3.6 [IF THE WARRANTS ARE SUBJECT TO ACCELERATION BY THE COMPANY, INSERT--
ACCELERATION OF WARRANTS BY THE COMPANY.

            (a) At any time on or after _______________, the Company shall have
the right to accelerate any or all Warrants at any time by causing them to
expire at the close of business on the day next preceding a specified date (the
"ACCELERATION DATE"), if the Market Price (as hereinafter defined) of the [title
of Preferred Stock purchasable through the exercise of the Warrants] equals or
exceeds __________ percent (__%) of the then effective Warrant Price on any
twenty Trading Days (as hereinafter defined) within a period of thirty
consecutive Trading Days ending no more than five Trading Days prior to the date
on which the Company gives notice to the Warrant Agent of its election to
accelerate the Warrants.

            (b) "Market Price" for each Trading Day shall be, if the [title of
Preferred Stock purchasable through the exercise of the Warrants] is listed or
admitted for trading on the New York Stock Exchange, the last reported sale
price, regular way (or, if no such price is reported, the average of the
reported closing bid and asked prices, regular way) of [title of Preferred Stock
purchasable through the exercise of the Warrants], in either case as reported on
the New York Stock Exchange Composite Tape or, if the [title of Preferred Stock
purchasable through the exercise of the Warrants]is not listed or admitted to
trading on the New York Stock Exchange, on the principal national securities
exchange on which the [title of Preferred Stock purchasable through the exercise
of the Warrants] is listed or admitted to trading or, if not listed or admitted
to trading on any national securities exchange, on the National Market System of
NASDAQ or, if not listed or admitted to trading on any national securities
exchange or quoted on the National Market System of NASDAQ, the average of the
closing high bid and low asked prices in the over-the-counter market, as
reported by NASDAQ, or such other system then in use, or if on any such date the
shares of [title of Preferred Stock purchasable through the exercise of the
Warrants] are not quoted by any such organization, the average of the closing
bid and asked prices as furnished by any New York Stock Exchange firm selected
from time to time by the Company for that purpose. "Trading Day" shall be each
Monday through Friday, other than any day on which securities are not traded in
the system or on the exchange that is the principal market for the [title of
Preferred Stock purchasable through the exercise of the Warrants], as determined
by the Board of Directors of the Company.

            (c) In the event of an acceleration of less than all of the
Warrants, the Warrant Agent shall select the Warrants to be accelerated by lot,
pro rata or in such other manner as it deems, in its discretion, to be fair and
appropriate.

            (d) Notice of an acceleration specifying the Acceleration Date shall
be sent by mail first class, postage prepaid, to each registered holder of a
Warrant Certificate representing a Warrant accelerated at such holder's address
appearing on the books of the Warrant Agent not more than sixty days nor less
than thirty days before the Acceleration Date. Such notice of an acceleration
also shall be given no more than twenty days, and no less than ten days, prior
to the mailing of notice to registered holders of Warrants pursuant to this
Section 3.6, by publication at least once in a newspaper of general circulation
in the City of New York.

                                       9.
<PAGE>

            (e) Any Warrant accelerated may be exercised until ________ p.m.,
[City] time, on the business day next preceding the Acceleration Date. The
Warrant Price shall be payable as provided in Section 2.]

                                    ARTICLE 4

                  EXCHANGE AND TRANSFER OF WARRANT CERTIFICATES

      4.1 EXCHANGE AND TRANSFER OF WARRANT CERTIFICATES. [If Other Securities
with Warrants which are immediately detachable--Upon] [If Other Securities
with Warrants which are not immediately detachable--Prior to the Detachable
Date, a Warrant Certificate may be exchanged or transferred only together with
the Other Security to which the Warrant Certificate was initially attached, and
only for the purpose of effecting or in conjunction with an exchange or transfer
of such Other Security. Prior to any Detachable Date, each transfer of the Other
Security shall operate also to transfer the related Warrant Certificates. After
the Detachable Date, upon] surrender at the corporate trust office of the
Warrant Agent, Warrant Certificates evidencing Warrants may be exchanged for
Warrant Certificates in other denominations evidencing such Warrants or the
transfer thereof may be registered in whole or in part; provided that such other
Warrant Certificates evidence Warrants for the same aggregate number of Warrant
Securities as the Warrant Certificates so surrendered. The Warrant Agent shall
keep, at its corporate trust office, books in which, subject to such reasonable
regulations as it may prescribe, it shall register Warrant Certificates and
exchanges and transfers of outstanding Warrant Certificates, upon surrender of
the Warrant Certificates to the Warrant Agent at its corporate trust office for
exchange or registration of transfer, properly endorsed or accompanied by
appropriate instruments of registration of transfer and written instructions for
transfer, all in form satisfactory to the Company and the Warrant Agent. No
service charge shall be made for any exchange or registration of transfer of
Warrant Certificates, but the Company may require payment of a sum sufficient to
cover any stamp or other tax or other governmental charge that may be imposed in
connection with any such exchange or registration of transfer. Whenever any
Warrant Certificates are so surrendered for exchange or registration of
transfer, an authorized officer of the Warrant Agent shall manually countersign
and deliver to the person or persons entitled thereto a Warrant Certificate or
Warrant Certificates duly authorized and executed by the Company, as so
requested. The Warrant Agent shall not be required to effect any exchange or
registration of transfer which will result in the issuance of a Warrant
Certificate evidencing a Warrant for a fraction of a Warrant Security or a
number of Warrants for a whole number of Warrant Securities and a fraction of a
Warrant Security. All Warrant Certificates issued upon any exchange or
registration of transfer of Warrant Certificates shall be the valid obligations
of the Company, evidencing the same obligations and entitled to the same
benefits under this Agreement as the Warrant Certificate surrendered for such
exchange or registration of transfer.

      4.2 TREATMENT OF HOLDERS OF WARRANT CERTIFICATES. [If Other Securities and
Warrants are not immediately detachable--Prior to the Detachable Date, the
Company, the Warrant Agent and all other persons may treat the owner of the
Other Security as the owner of the Warrant Certificates initially attached
thereto for any purpose and as the person entitled to exercise the rights
represented by the Warrants evidenced by such Warrant Certificates, any notice
to the contrary notwithstanding. After the Detachable Date and prior to due
presentment of a Warrant Certificate for registration of transfer, the] [T]he
Company, the Warrant Agent and

                                      10.
<PAGE>

all other persons may treat the registered holder of a Warrant Certificate as
the absolute owner thereof for any purpose and as the person entitled to
exercise the rights represented by the Warrants evidenced thereby, any notice to
the contrary notwithstanding.

      4.3 CANCELLATION OF WARRANT CERTIFICATES. Any Warrant Certificate
surrendered for exchange, registration of transfer or exercise of the Warrants
evidenced thereby shall, if surrendered to the Company, be delivered to the
Warrant Agent and all Warrant Certificates surrendered or so delivered to the
Warrant Agent shall be promptly canceled by the Warrant Agent and shall not be
reissued and, except as expressly permitted by this Agreement, no Warrant
Certificate shall be issued hereunder in exchange therefor or in lieu thereof.
The Warrant Agent shall deliver to the Company from time to time or otherwise
dispose of canceled Warrant Certificates in a manner satisfactory to the
Company.

                                   ARTICLE 5

                          CONCERNING THE WARRANT AGENT

      5.1 WARRANT AGENT. The Company hereby appoints ____________ as Warrant
Agent of the Company in respect of the Warrants and the Warrant Certificates
upon the terms and subject to the conditions herein set forth, and ___________
hereby accepts such appointment. The Warrant Agent shall have the powers and
authority granted to and conferred upon it in the Warrant Certificates and
hereby and such further powers and authority to act on behalf of the Company as
the Company may hereafter grant to or confer upon it. All of the terms and
provisions with respect to such powers and authority contained in the Warrant
Certificates are subject to and governed by the terms and provisions hereof.

      5.2 CONDITIONS OF WARRANT AGENT'S OBLIGATIONS. The Warrant Agent accepts
its obligations herein set forth upon the terms and conditions hereof, including
the following to all of which the Company agrees and to all of which the rights
hereunder of the holders from time to time of the Warrant Certificates shall be
subject:

            (a) COMPENSATION AND INDEMNIFICATION. The Company agrees promptly to
pay the Warrant Agent the compensation to be agreed upon with the Company for
all services rendered by the Warrant Agent and to reimburse the Warrant Agent
for reasonable out-of-pocket expenses (including reasonable counsel fees)
incurred without negligence, bad faith or willful misconduct by the Warrant
Agent in connection with the services rendered hereunder by the Warrant Agent.
The Company also agrees to indemnify the Warrant Agent for, and to hold it
harmless against, any loss, liability or expense incurred without negligence,
bad faith or willful misconduct on the part of the Warrant Agent, arising out of
or in connection with its acting as Warrant Agent hereunder, including the
reasonable costs and expenses of defending against any claim of such liability.

            (b) AGENT FOR THE COMPANY. In acting under this Warrant Agreement
and in connection with the Warrant Certificates, the Warrant Agent is acting
solely as agent of the Company and does not assume any obligations or
relationship of agency or trust for or with any of the holders of Warrant
Certificates or beneficial owners of Warrants.

                                      11.
<PAGE>

            (c) COUNSEL. The Warrant Agent may consult with counsel satisfactory
to it, which may include counsel for the Company, and the written advice of such
counsel shall be full and complete authorization and protection in respect of
any action taken, suffered or omitted by it hereunder in good faith and in
accordance with the advice of such counsel.

            (d) DOCUMENTS. The Warrant Agent shall be protected and shall incur
no liability for or in respect of any action taken or omitted by it in reliance
upon any Warrant Certificate, notice, direction, consent, certificate,
affidavit, statement or other paper or document reasonably believed by it to be
genuine and to have been presented or signed by the proper parties.

            (e) CERTAIN TRANSACTIONS. The Warrant Agent, and its officers,
directors and employees, may become the owner of, or acquire any interest in,
Warrants, with the same rights that it or they would have if it were not the
Warrant Agent hereunder, and, to the extent permitted by applicable law, it or
they may engage or be interested in any financial or other transaction with the
Company and may act on, or as depositary, trustee or agent for, any committee or
body of holders of Warrant Securities or other obligations of the Company as
freely as if it were not the Warrant Agent hereunder. Nothing in this Warrant
Agreement shall be deemed to prevent the Warrant Agent from acting as trustee
under any indenture to which the Company is a party.

            (f) NO LIABILITY FOR INTEREST. Unless otherwise agreed with the
Company, the Warrant Agent shall have no liability for interest on any monies at
any time received by it pursuant to any of the provisions of this Agreement or
of the Warrant Certificates.

            (g) NO LIABILITY FOR INVALIDITY. The Warrant Agent shall have no
liability with respect to any invalidity of this Agreement or any of the Warrant
Certificates (except as to the Warrant Agent's countersignature thereon).

            (h) NO RESPONSIBILITY FOR REPRESENTATIONS. The Warrant Agent shall
not be responsible for any of the recitals or representations herein or in the
Warrant Certificates (except as to the Warrant Agent's countersignature
thereon), all of which are made solely by the Company.

            (i) NO IMPLIED OBLIGATIONS. The Warrant Agent shall be obligated to
perform only such duties as are herein and in the Warrant Certificates
specifically set forth and no implied duties or obligations shall be read into
this Agreement or the Warrant Certificates against the Warrant Agent. The
Warrant Agent shall not be under any obligation to take any action hereunder
which may tend to involve it in any expense or liability, the payment of which
within a reasonable time is not, in its reasonable opinion, assured to it. The
Warrant Agent shall not be accountable or under any duty or responsibility for
the use by the Company of any of the Warrant Certificates authenticated by the
Warrant Agent and delivered by it to the Company pursuant to this Agreement or
for the application by the Company of the proceeds of the Warrant Certificates.
The Warrant Agent shall have no duty or responsibility in case of any default by
the Company in the performance of its covenants or agreements contained herein
or in the Warrant Certificates or in the case of the receipt of any written
demand from a holder of a Warrant Certificate with respect to such default,
including, without limiting the generality of the

                                      12.
<PAGE>

foregoing, any duty or responsibility to initiate or attempt to initiate any
proceedings at law or otherwise or, except as provided in Section 6.2 hereof, to
make any demand upon the Company.

      5.3 RESIGNATION AND APPOINTMENT OF SUCCESSOR.

            (a) The Company agrees, for the benefit of the holders from time to
time of the Warrant Certificates, that there shall at all times be a Warrant
Agent hereunder until all the Warrants have been exercised or are no longer
exercisable.

            (b) The Warrant Agent may at any time resign as agent by giving
written notice to the Company of such intention on its part, specifying the date
on which its desired resignation shall become effective; provided that such date
shall not be less than three months after the date on which such notice is given
unless the Company otherwise agrees. The Warrant Agent hereunder may be removed
at any time by the filing with it of an instrument in writing signed by or on
behalf of the Company and specifying such removal and the intended date when it
shall become effective. Such resignation or removal shall take effect upon the
appointment by the Company, as hereinafter provided, of a successor Warrant
Agent (which shall be a bank or trust company authorized under the laws of the
jurisdiction of its organization to exercise corporate trust powers) and the
acceptance of such appointment by such successor Warrant Agent. The obligation
of the Company under Section 5.2(a) shall continue to the extent set forth
therein notwithstanding the resignation or removal of the Warrant Agent.

            (c) In case at any time the Warrant Agent shall resign, or shall be
removed, or shall become incapable of acting, or shall be adjudged a bankrupt or
insolvent, or shall commence a voluntary case under the Federal bankruptcy laws,
as now or hereafter constituted, or under any other applicable Federal or state
bankruptcy, insolvency or similar law or shall consent to the appointment of or
taking possession by a receiver, custodian, liquidator, assignee, trustee,
sequestrator (or other similar official) of the Warrant Agent or its property or
affairs, or shall make an assignment for the benefit of creditors, or shall
admit in writing its inability to pay its debts generally as they become due, or
shall take corporate action in furtherance of any such action, or a decree or
order for relief by a court having jurisdiction in the premises shall have been
entered in respect of the Warrant Agent in an involuntary case under the Federal
bankruptcy laws, as now or hereafter constituted, or any other applicable
Federal or state bankruptcy, insolvency or similar law, or a decree or order by
a court having jurisdiction in the premises shall have been entered for the
appointment of a receiver, custodian, liquidator, assignee, trustee,
sequestrator (or similar official) of the Warrant Agent or of its property or
affairs, or any public officer shall take charge or control of the Warrant Agent
or of its property or affairs for the purpose of rehabilitation, conservation,
winding up or liquidation, a successor Warrant Agent, qualified as aforesaid,
shall be appointed by the Company by an instrument in writing, filed with the
successor Warrant Agent. Upon the appointment as aforesaid of a successor
Warrant Agent and acceptance by the successor Warrant Agent of such appointment,
the Warrant Agent shall cease to be Warrant Agent hereunder.

            (d) Any successor Warrant Agent appointed hereunder shall execute,
acknowledge and deliver to its predecessor and to the Company an instrument
accepting such appointment hereunder, and thereupon such successor Warrant
Agent, without any further act, deed or conveyance, shall become vested with all
the authority, rights, powers, trusts,

                                      13.
<PAGE>

immunities, duties and obligations of such predecessor with like effect as if
originally named as Warrant Agent hereunder, and such predecessor, upon payment
of its charges and disbursements then unpaid, shall thereupon become obligated
to transfer, deliver and pay over, and such successor Warrant Agent shall be
entitled to receive, all monies, securities and other property on deposit with
or held by such predecessor, as Warrant Agent hereunder.

            (e) Any corporation into which the Warrant Agent hereunder may be
merged or converted or any corporation with which the Warrant Agent may be
consolidated, or any corporation resulting from any merger, conversion or
consolidation to which the Warrant Agent shall be a party, or any corporation to
which the Warrant Agent shall sell or otherwise transfer all or substantially
all the assets and business of the Warrant Agent, provided that it shall be
qualified as aforesaid, shall be the successor Warrant Agent under this
Agreement without the execution or filing of any paper or any further act on the
part of any of the parties hereto.

                                   ARTICLE 6

                                 MISCELLANEOUS

      6.1 AMENDMENT. This Agreement may be amended by the parties hereto,
without the consent of the holder of any Warrant Certificate, for the purpose of
curing any ambiguity, or of curing, correcting or supplementing any defective
provision contained herein, or making any other provisions with respect to
matters or questions arising under this Agreement as the Company and the Warrant
Agent may deem necessary or desirable; provided that such action shall not
materially adversely affect the interests of the holders of the Warrant
Certificates.

      6.2 NOTICES AND DEMANDS TO THE COMPANY AND WARRANT AGENT. If the Warrant
Agent shall receive any notice or demand addressed to the Company by the holder
of a Warrant Certificate pursuant to the provisions of the Warrant Certificates,
the Warrant Agent shall promptly forward such notice or demand to the Company.

      6.3 ADDRESSES. Any communication from the Company to the Warrant Agent
with respect to this Agreement shall be addressed to ______________________,
Attention: ____________ and any communication from the Warrant Agent to the
Company with respect to this Agreement shall be addressed to Onyx
Pharmaceuticals, Inc., 2100 Powell Street, Emeryville, CA 94608, Attention:
General Counsel (or such other address as shall be specified in writing by the
Warrant Agent or by the Company).

      6.4 GOVERNING LAW. This Agreement and each Warrant Certificate issued
hereunder shall be governed by and construed in accordance with the laws of the
State of New York.

      6.5 DELIVERY OF PROSPECTUS. The Company shall furnish to the Warrant Agent
sufficient copies of a prospectus meeting the requirements of the Securities Act
of 1933, as amended, relating to the Warrant Securities deliverable upon
exercise of the Warrants (the "PROSPECTUS"), and the Warrant Agent agrees that
upon the exercise of any Warrant, the Warrant Agent will deliver to the holder
of the Warrant Certificate evidencing such Warrant, prior to or concurrently
with the delivery of the Warrant Securities issued upon such exercise, a
Prospectus.

                                      14.
<PAGE>

      The Warrant Agent shall not, by reason of any such delivery, assume any
responsibility for the accuracy or adequacy of such Prospectus.

      6.6 OBTAINING OF GOVERNMENTAL APPROVALS. The Company will from time to
time take all action which may be necessary to obtain and keep effective any and
all permits, consents and approvals of governmental agencies and authorities and
securities act filings under United States Federal and state laws (including
without limitation a registration statement in respect of the Warrants and
Warrant Securities under the Securities Act of 1933, as amended), which may be
or become requisite in connection with the issuance, sale, transfer, and
delivery of the Warrant Securities issued upon exercise of the Warrants, the
issuance, sale, transfer and delivery of the Warrants or upon the expiration of
the period during which the Warrants are exercisable.

      6.7 PERSONS HAVING RIGHTS UNDER WARRANT AGREEMENT. Nothing in this
Agreement shall give to any person other than the Company, the Warrant Agent and
the holders of the Warrant Certificates any right, remedy or claim under or by
reason of this Agreement.

      6.8 HEADINGS. The descriptive headings of the several Articles and
Sections of this Agreement are inserted for convenience only and shall not
control or affect the meaning or construction of any of the provisions hereof.

      6.9 COUNTERPARTS. This Agreement may be executed in any number of
counterparts, each of which as so executed shall be deemed to be an original,
but such counterparts shall together constitute but one and the same instrument.

      6.10 INSPECTION OF AGREEMENT. A copy of this Agreement shall be available
at all reasonable times at the principal corporate trust office of the Warrant
Agent for inspection by the holder of any Warrant Certificate. The Warrant Agent
may require such holder to submit his Warrant Certificate for inspection by it.

                                      15.
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed, all as of the day and year first above written.

                                         ONYX PHARMACEUTICALS, INC.

                                         By:   _______________________________

                                         Its:  _______________________________

Attest:

___________________________

___________________________

                                         Warrant Agent

                                         By:   _______________________________

                                         Its:  _______________________________

Attest:

___________________________

___________________________

              [SIGNATURE PAGE TO PREFERRED STOCK WARRANT AGREEMENT]

                                      16.
<PAGE>

                                    EXHIBIT A

                           FORM OF WARRANT CERTIFICATE

                          [FACE OF WARRANT CERTIFICATE]

[[Form if Warrants are attached to Other Securities and are not immediately
detachable.]

[Prior to ______________, this Warrant Certificate cannot be transferred or
exchanged unless attached to a [Title of Other Securities].]

[Form of Legend if Warrants are not immediately exercisable.] [Prior to
________, Warrants evidenced by this Warrant Certificate cannot be exercised.]

      EXERCISABLE ONLY IF COUNTERSIGNED BY THE WARRANT AGENT AS PROVIDED HEREIN

           VOID AFTER _________ P.M., [CITY] TIME, ON _______________.

                                      17.
<PAGE>

                           ONYX PHARMACEUTICALS, INC.

                        WARRANT CERTIFICATE REPRESENTING
                              WARRANTS TO PURCHASE
                          [TITLE OF WARRANT SECURITIES]

No. __________                                                         Warrants

      This certifies that ____________ or registered assigns is the registered
owner of the above indicated number of Warrants, each Warrant entitling such
owner [if Warrants are attached to Other Securities and are not immediately
detachable--, subject to the registered owner qualifying as a "Holder" of this
Warrant Certificate, as hereinafter defined),] to purchase, at any time [after
____ p.m., [City] time, on _________ and] on or before ____ p.m., [City] time,
on ___________ shares of [Title of Warrant Securities] (the "WARRANT
SECURITIES"), of Onyx Pharmaceuticals, Inc. (the "COMPANY") on the following
basis: during the period from ____________, through and including ____________,
the exercise price per Warrant Security will be $_________, subject to
adjustment as provided in the Warrant Agreement (as hereinafter defined) (the
"WARRANT PRICE"). The Holder may exercise the Warrants evidenced hereby by
providing certain information set forth on the back hereof and by paying in
full, in lawful money of the United States of America, [in cash or by certified
check or official bank check in New York Clearing House funds][by bank wire
transfer in immediately available funds], the Warrant Price for each Warrant
Security with respect to which this Warrant is exercised to the Warrant Agent
(as hereinafter defined) and by surrendering this Warrant Certificate, with the
purchase form on the back hereof duly executed, at the corporate trust office of
[name of Warrant Agent], or its successor as warrant agent (the "WARRANT
AGENT"), which is, on the date hereof, at the address specified on the reverse
hereof, and upon compliance with and subject to the conditions set forth herein
and in the Warrant Agreement (as hereinafter defined).

      The term "HOLDER" as used herein shall mean [if Warrants are attached to
Other Securities and are not immediately detachable--prior to ______________
(the "DETACHABLE DATE"), the registered owner of the Company's [title of Other
Securities] to which this Warrant Certificate was initially attached, and after
such Detachable Date,] the person in whose name at the time this Warrant
Certificate shall be registered upon the books to be maintained by the Warrant
Agent for that purpose pursuant to Section 4 of the Warrant Agreement.

      The Warrants evidenced by this Warrant Certificate may be exercised to
purchase a whole number of Warrant Securities in registered form. Upon any
exercise of fewer than all of the Warrants evidenced by this Warrant
Certificate, there shall be issued to the Holder hereof a new Warrant
Certificate evidencing Warrants for the number of Warrant Securities remaining
unexercised.

      This Warrant Certificate is issued under and in accordance with the
Warrant Agreement dated as of _______________ (the "WARRANT AGREEMENT"), between
the Company and the Warrant Agent and is subject to the terms and provisions
contained in the Warrant Agreement, to all of which terms and provisions the
Holder of this Warrant Certificate consents by acceptance hereof. Copies of the
Warrant Agreement are on file at the above-mentioned office of the Warrant
Agent.

                                      18.
<PAGE>

      [If Warrants are attached to Other Securities and are not immediately
detachable--Prior to the Detachable Date, this Warrant Certificate may be
exchanged or transferred only together with the [Title of Other Securities] (the
"OTHER SECURITIES") to which this Warrant Certificate was initially attached,
and only for the purpose of effecting or in conjunction with, an exchange or
transfer of such Other Security. Additionally, on or prior to the Detachable
Date, each transfer of such Other Security on the register of the Other
Securities shall operate also to transfer this Warrant Certificate. After such
date, transfer of this] [If Warrants are attached to Other Securities and are
immediately detachable--Transfer of this] Warrant Certificate may be
registered when this Warrant Certificate is surrendered at the corporate trust
office of the Warrant Agent by the registered owner or such owner's assigns, in
the manner and subject to the limitations provided in the Warrant Agreement.

      [If Other Securities with Warrants which are not immediately detachable--
Except as provided in the immediately preceding paragraph, after] [If Other
Securities with Warrants which are immediately detachable or Warrants alone--
After] countersignature by the Warrant Agent and prior to the expiration of this
Warrant Certificate, this Warrant Certificate may be exchanged at the corporate
trust office of the Warrant Agent for Warrant Certificates representing Warrants
for the same aggregate number of Warrant Securities.

      This Warrant Certificate shall not entitle the Holder hereof to any of the
rights of a holder of the Warrant Securities, including, without limitation, the
right to receive payments of dividends or distributions, if any, on the Warrant
Securities (except to the extent set forth in the Warrant Agreement) or to
exercise any voting rights.

      Reference is hereby made to the further provisions of this Warrant
Certificate set forth on the reverse hereof, which further provisions shall for
all purposes have the same effect as if set forth at this place.

      This Warrant Certificate shall be governed by and construed in accordance
with the laws of the State of New York.

      This Warrant Certificate shall not be valid or obligatory for any purpose
until countersigned by the Warrant Agent.

                                      19.
<PAGE>

         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
in its name and on its behalf by the facsimile signatures of its duly authorized
officers.

Dated: ____________________

                                               ONYX PHARMACEUTICALS, INC.

                                               By:  __________________________

                                               Its: __________________________

Attest:

___________________________

___________________________

                                               Countersigned:

                                               ________________________________
                                               As Warrant Agent

                                               By: ____________________________
                                                        Authorized Signature

Attest:

___________________________

___________________________

                                      20.
<PAGE>

                        [REVERSE OF WARRANT CERTIFICATE]

                     (INSTRUCTIONS FOR EXERCISE OF WARRANT)

      To exercise any Warrants evidenced hereby for Warrant Securities (as
hereinafter defined), the Holder must pay, in lawful money of the United States
of America, [in cash or by certified check or official bank check in New York
Clearing House funds] [by bank wire transfer in immediately available funds],
the Warrant Price in full for Warrants exercised, to [Warrant Agent] [address of
Warrant Agent], Attn: ____________, which payment must specify the name of the
Holder and the number of Warrants exercised by such Holder. In addition, the
Holder must complete the information required below and present this Warrant
Certificate in person or by mail (certified or registered mail is recommended)
to the Warrant Agent at the appropriate address set forth above. This Warrant
Certificate, completed and duly executed, must be received by the Warrant Agent
within five business days of the payment.

                   (To be executed upon exercise of Warrants)

                                      21.
<PAGE>

      The undersigned hereby irrevocably elects to exercise ___________
Warrants, evidenced by this Warrant Certificate, to purchase _____________
shares of the [Title of Warrant Securities] (the "WARRANT SECURITIES"), of Onyx
Pharmaceuticals, Inc. and represents that he has tendered payment for such
Warrant Securities, in lawful money of the United States of America, [in cash or
by certified check or official bank check in New York Clearing House funds] [by
bank wire transfer in immediately available funds], to the order of Onyx
Pharmaceuticals, Inc., c/o [insert name and address of Warrant Agent], in the
amount of $___________ in accordance with the terms hereof. The undersigned
requests that said Warrant Securities be in fully registered form in the
authorized denominations, registered in such names and delivered all as
specified in accordance with the instructions set forth below.

      If the number of Warrants exercised is less than all of the Warrants
evidenced hereby, the undersigned requests that a new Warrant Certificate
evidencing the Warrants for the number of Warrant Securities remaining
unexercised be issued and delivered to the undersigned unless otherwise
specified in the instructions below.

Dated    ___________________             Name _________________________________
                                              (Please Print)

Address  ___________________

_____________________________________________________________
(Insert Social Security or Other Identifying Number of Holder)

Signature Guaranteed
                                         _______________________________________
                                         Signature

      (Signature must conform in all respects to name of holder as specified on
the face of this Warrant Certificate and must bear a signature guarantee by a
bank, trust company or member broker of the New York, Midwest or Pacific Stock
Exchange).

                                      22.
<PAGE>

This Warrant may be exercised at the following addresses:

By hand at        _____________________________________________________________

                  _____________________________________________________________

                  _____________________________________________________________

By mail at        _____________________________________________________________

                  _____________________________________________________________

                  _____________________________________________________________

[Instructions as to form and delivery of Warrant Securities and, if applicable,
Warrant Certificates evidencing Warrants for the number of Warrant Securities
remaining unexercised--complete as appropriate.]

                                      23.
<PAGE>

                                   ASSIGNMENT

      [Form of assignment to be executed if Warrant Holder desires to transfer
Warrant)

      FOR VALUE RECEIVED,             hereby sells, assigns and transfers unto:
________________________________

________________________________

________________________________

________________________________       _______________________________________

(Please print name and address        Please insert Social Security or other
including zip code)                   identifying number

the right represented by the within Warrant to purchase __________ shares of
[Title of Warrant Securities] of Onyx Pharmaceuticals, Inc. to which the within
Warrant relates and appoints ____________ attorney to transfer such right on the
books of the Warrant Agent with full power of substitution in the premises.

Dated     _____________________          ______________________________________
                                         Signature

(Signature must conform in all respects to name of holder as specified on the
face of the Warrant)

Signature Guaranteed

______________________________________

                                      24.