CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY 
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND 
EXCHANGE COMMISSION PURSUANT TO RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 
1934, AS AMENDED.

                                                                 EXHIBIT 10.24

                      AMENDMENT TO COLLABORATION AGREEMENT
                                     BETWEEN
                ONYX PHARMACEUTICALS, INC. AND BAYER CORPORATION

         This Amendment to the Collaboration Agreement (the "Second 
Amendment") is dated February 1, 1999 ("the Effective Date of the Second 
Amendment") by and between ONYX PHARMACEUTICALS, Inc., a California 
corporation having its principal place of business in Richmond, California 
("Onyx") and BAYER CORPORATION, an Indiana corporation having its principal 
place of business in Pittsburgh, Pennsylvania ("Bayer"). Bayer and Onyx may 
be referred to herein individually as "Party," or collectively, as the 
"Parties."

                                    RECITALS

         WHEREAS, Onyx and Bayer (under the name Miles Inc., the prior name 
of Bayer) entered into a Collaboration Agreement dated April 22, 1994, as 
amended on April 24, 1996 (the "First Amendment") (such agreement as amended 
by the First Amendment being referred to herein as the "Collaboration 
Agreement"); and

         WHEREAS, in connection with the end of the Research Term, Onyx and 
Bayer desire to amend and modify the terms of the Collaboration Agreement so 
as to: (i) set forth certain understandings regarding the possible 
development of [*]; (ii) more precisely define the aspects of the Parties' 
research following the end of the Research Term which will, and will not, be 
within the scope of the Collaboration Agreement; and (iii) more precisely 
define Onyx' remaining Research obligations during the balance of the 
Research Term;

         NOW THEREFORE, in consideration of the covenants contained in this 
Amendment, the Parties agree as follows:

         1.   CAPITALIZED  TERMS PREVIOUSLY  DEFINED. Capitalized terms used 
but not defined herein shall have the same meanings given to them in the 
Collaboration Agreement.

         2.   AMENDMENT OF DEFINED TERM: COLLABORATION COMPOUND. Section 1.9 
of the Collaboration Agreement is hereby amended to read in its entirety as 
follows:

              1.9 "COLLABORATION COMPOUND" means, except as provided below,
         any composition of matter that is discovered, identified or synthesized
         by or on behalf of Onyx or Bayer or an Affiliate of either of them, and
         is recognized for its activity for inhibiting the activity of a target
         within the Residual Field of Collaborative Research prior to the date
         which is the earlier of (a) the date such target is removed from the
         Residual Field of Collaborative Research pursuant to Section 12 below,
         or (b) the first anniversary of the end of the Research Term.


                                      1.



         As used herein, the activity of a composition of matter for 
inhibiting a target within the Residual Field of Collaborative Research will 
be "recognized" if it satisfies that standard for a ras positive set forth in 
Exhibit D, or other specific activity in a particular assay or assays within 
the Residual Field of Collaborative Research established by the JRDC from 
time to time pursuant to Section 6.3.

         Notwithstanding the foregoing, the term "Collaboration Compound" 
shall not include:

                   (a) any composition of matter marketed by Bayer 
         or an Affiliate of Bayer as of April 22, 1994 or as to which Bayer 
         or an Affiliate of Bayer is conducting human clinical trials or 
         have approved the commencement of preclinical development (as 
         determined by the appropriate committee of Bayer or an Affiliate of 
         Bayer), as of April 22, 1994; or

                   (b) any composition of matter owned by Bayer or 
         Onyx or an Affiliate of either of them that could become subject to 
         this Agreement by reason of an expansion of the Field of 
         Collaborative Research after April 22, 1994 but as to which 
         marketing rights have been granted to a Third Party prior to such 
         expansion; or

                   (c) any composition of matter that is a Back-Up 
         Compound after [*] years following the end of the Research Term. 
         Rights in such compounds after such [*] year period shall be 
         allocated as set forth on Exhibit A(3).

         3.   AMENDMENT OF DEFINED TERM: POST-COLLABORATION COMPOUND. Section 
1.39 of the Collaboration Agreement is hereby amended to read in its entirety 
as follows:

              1.39   "POST-COLLABORATION COMPOUND" means any composition of
         matter synthesized, identified or discovered by Onyx or Bayer:

                  (a) that is contained within a chemical genus as defined 
         in any pending or issued claim of any unexpired Bayer Patent or 
         Onyx Patent filed in the United States, the United Kingdom, France, 
         or Germany or in the European Patent Office and as to which at 
         least one member of such chemical genus is a Collaboration 
         Compound, and

                   (b) that is recognized for its activity in inhibiting a 
         target within the Residual Field of the Collaborative Research, as 
         defined in Section 1.55, by Onyx or Bayer during the [*] year 
         period after the end of the Research Term, pursuant to Section 
         9.6(d) (at a royalty rate pursuant to Section 16.6).

         4.   ADDITIONAL DEFINED TERM. The Collaboration Agreement is hereby 
amended to add the following additional defined term:

              1.55   "RESIDUAL FIELD OF COLLABORATIVE RESEARCH" means, subject
         to Section 12 of the Second Amendment, the following targets: (i) [*],
         (ii) [*]; (iii) [*]; (iv) [*]; (v) [*]; and (vi) those targets, if any,
         from the [*] Project which the JRDC designates during the [*] following
         the end of the Research Term as being within the Residual Field of
         Collaborative Research.


[*] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY 
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND 
EXCHANGE COMMISSION PURSUANT TO RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 
1934, AS AMENDED.

                                      2.



         5.   ADDITIONAL DEFINED TERM. The Collaboration Agreement is hereby 
amended to add the following additional defined term:

              1.56   "[*] PROJECT" means the project underway as of the
         Effective Date of the Second Amendment, between Onyx and [*] to
         identify [*] is specifically [*] in response to the presence of an [*]
         in human tissue culture cell lines as determined under [*] conditions.
         Such cell lines shall include the [*] cell lines [*] cell line) and [*]
         cell line). In this project, these [*] are being compared to those
         obtained from analysis of the [*] cell lines. This project will be
         limited to the identity of those [*] represented on the [*], available
         from [*].

         6.   DESIGNATION OF [*]. Onyx shall provide to the JRDC the data 
obtained from the [*] Project, including the list of [*] whose [*] is [*] 
under the specified conditions, promptly following receipt of such data by 
Onyx. Within thirty (30) days following such delivery of data, the JRDC shall 
meet to designate which of such [*], if any, shall be included within the 
Residual Field of Collaborative Research. If the JRDC elects to include any 
[*] studied in the [*] Project within the Residual Field of Collaborative 
Research, it shall also define a program of follow-up research activities by 
the Parties to pursue such [*] of interest. Whether or not the JRDC elects to 
include within the Residual Field of Collaborative Research any of the [*] 
studied in the course of the [*] Project, Onyx and Bayer shall each own an 
undivided one-half interest in the data obtained from the [*] Project, and 
each Party shall be entitled to conduct work related to such [*] and 
commercialize resulting products without obligation to the other, unless the 
resulting products contain Collaboration Compounds or Post-Collaboration 
Compounds.

         7.   AMENDMENT TO PARAGRAPH 9.6(d). Paragraph 9.6(d) is amended to 
change the last phrase of the last sentence in the paragraph from "shall be 
done by Onyx" to "may be done by either Party."

         8.   [*] COLLABORATION COMPOUNDS. Onyx and Bayer agree that any and 
all [*]Collaboration Compounds that are designated by the JRDC as Development 
Compounds for Co-Development shall be treated for purposes of the 
Collaboration Agreement as having been so designated prior to the end of the 
Research Term pursuant to Section 11.4 of the Collaboration Agreement, 
regardless of when such [*]Collaboration Compounds are designated Development 
Compounds for Co-Development. Onyx and Bayer further agree that any [*] 
Collaboration Compounds selected by the JRDC as Back-Up Compounds shall be 
treated as having been so designated prior to the end of the Research Term 
pursuant to Section 11.4 of the Collaboration Agreement, regardless of when 
such [*] Collaboration Compounds are selected as Back-Up Compounds.

         9.   DEVELOPMENT GUIDELINES. In order to insure that both Parties 
have every incentive to invest in the success of the joint effort 
contemplated by this Agreement, the Parties agree as follows:

                   (a) In the event the JRDC designates a [*] Collaboration 
         Compound as a Development Compound prior to June 30, 1999, the 
         Parties agree that so long as Onyx and Bayer are engaged in 
         Co-Development or Bayer is engaged in development of at least one 
         [*] Development Compound with Bayer diligently pursuing or 
         participating in


[*] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY 
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND 
EXCHANGE COMMISSION PURSUANT TO RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 
1934, AS AMENDED.

                                      3.



         pursuit of development activities to obtain marketing approval, or 
         Bayer is marketing a Product containing such a Development 
         Compound, then Bayer shall not be obligated to [*] more than [*] 
         Development Compound at any one time, and Onyx shall not pursue [*]
         under the Agreement, including but not limited to Paragraphs 7.3, 
         9.6, or Article 12 with respect to [*].

                   (b) If the JRDC at any time in the future designates one 
         or more additional Collaboration Compounds as Development 
         Compounds, and Bayer agrees that such compound(s) will be treated 
         for purposes of the Collaboration Agreement as if they had been 
         designated for Co-Development prior to the end of the Research 
         Term, and provided Onyx has not at the time of such JRDC 
         designation and Bayer agreement already commenced development of a 
         compound directed against the molecular target in question, the 
         Parties agree that so long as Onyx and Bayer are engaged in 
         Co-Development or Bayer is engaged in development of [*] with Bayer 
         diligently pursuing or participating in pursuit of development 
         activities to obtain marketing approval, or Bayer is marketing a 
         Product containing such a Development Compound, then Bayer shall 
         not be obligated to [*] more than [*] at any one time, and Onyx 
         shall not pursue [*] under the Agreement, including but not limited 
         to Paragraphs 7.3, 9.6, or Article 12 with respect to that target. 
         In the event a compound is active against two (2) or more targets 
         contained in the Residual Field of Collaborative Research, the 
         development of said compound with respect to one (1) of said 
         targets will satisfy the requirements of this paragraph with 
         respect to all of such targets.

         10.  ACQUISITION OF COMPOUNDS FROM [*]. During the Research Term, 
the Parties evaluated for possible acquisition under the Agreement a compound 
in the field of [*] owned by [*]. Onyx agrees that it will not participate 
further in the acquisition or development of this compound, Bayer is free to 
enter into an agreement with [*] for the development of one or more 
compound(s) in the field of [*].

         11.  ONYX' AND BAYER'S RIGHTS TO CONDUCT INDEPENDENT DISCOVERY. 
Commencing February 1, 1999, each of Onyx and Bayer shall have the right to 
engage in the independent discovery of inhibitors of Ras Function independent 
of the other Party outside the Residual Field of Collaborative Research. 
Commencing on such date, any compositions of matter discovered by either 
Party that inhibit Ras Function outside the Residual Field of Collaborative 
Research shall be outside the scope of the Collaboration Agreement, unless 
such compositions of matter fall within the definition of Collaboration 
Compounds or Post-Collaboration Compounds with respect to the Residual Field 
of Collaborative Research. No licenses are granted for such independent 
discovery activities except as set forth in Article 4 of the Collaboration 
Agreement.

         12.  TARGETS REMOVED FROM THE RESIDUAL FIELD OF COLLABORATIVE 
RESEARCH. Individual targets contained within the Residual Field of 
Collaborative Research as of the Effective Date of the Second Amendment 
("Residual Targets") shall be removed from the Residual Field of 
Collaborative Research if, on or before August 1, 1999, such targets are 
screened against a representative set of Bayer compounds and, on the basis of 
the results of such screening, thc JRDC determines (with the concurrence of 
representatives of both Parties) that such results do not justify the 
designation of a strategic Analoging Program related to such Residual Target.


[*] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY 
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND 
EXCHANGE COMMISSION PURSUANT TO RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 
1934, AS AMENDED.

                                      4.



         13.  REMAINING ONYX RESEARCH OBLIGATIONS. Pursuant to the Research 
Program, Onyx shall provide to Bayer, as soon as practicable after the 
Effective Date of the Second Amendment, the new assays and materials outlined 
on Exhibit E to this Amendment (to the extent not already delivered to 
Bayer). Within thirty (30) days after such delivery Bayer will pay Onyx any 
final payment due in support of the research under thc Research Term. Onyx 
shall be [*] to provide or account for a specific number of [*] under the 
Collaboration Agreement during the last [*] of the Research Term.

         14.  NEW NAME AND ADDRESS FOR NOTICE FOR BAYER CORPORATION. In 
Paragraph 28.7, "Notices", the name and address for notice to Bayer is 
amended to read as follows:

              BAYER CORPORATION
              Pharmaceutical Division
              400 Morgan Lane
              West Haven, CT 06516
              Attention:  VP, Law & Patents
              Telephone:  (203) 812-2401
              Telecopy:   (203) 812-2795

         with a copy to Jones, Day, Reavis & Pogue as previously set forth.

         15.  FULL FORCE AND EFFECT OF AGREEMENT. The Collaboration 
Agreement, as modified by the First Amendment and Second Amendment, 
constitutes the entire agreement of the Parties on the subject matter hereof. 
The Collaboration Agreement, as modified hereby, remains in full force and 
effect.



- ------------------------------------------------------------ ---------------------------------------------------------
ONYX PHARMACEUTICALS, INC.                                   BAYER CORPORATION
- ------------------------------------------------------------ ---------------------------------------------------------
                                                          
By:  /s/   Hollings C. Renton                                By:    /s/   Michael J. Berendt
     ------------------------------------------------             ------------------------------------------------
- ------------------------------------------------------------ ---------------------------------------------------------
Name:  Hollings C. Renton                                    Name:  Michael J. Berendt, Ph.D.
- ------------------------------------------------------------ ---------------------------------------------------------
Title:  President and Chief Executive Officer                Title:  Sr. VP, Pharmaceutical Research
- ------------------------------------------------------------ ---------------------------------------------------------
Date:  February 10, 1999                                     Date:  March 1, 1999
- ------------------------------------------------------------ ---------------------------------------------------------



[*] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY 
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND 
EXCHANGE COMMISSION PURSUANT TO RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 
1934, AS AMENDED.

                                      5.



                                    EXHIBIT E

                              ASSAYS AND MATERIALS
                        TO BE DELIVERED TO BAYER BY ONYX

[*] Assay

[*] Assay

[*] Assay

[*] Assay

[*] Assay

Results of [*] Project


[*] = CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY 
BRACKETS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND 
EXCHANGE COMMISSION PURSUANT TO RULE 24b-2 OF THE SECURITIES EXCHANGE ACT OF 
1934, AS AMENDED.

                                      6.