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ONYX PHARMACEUTICALS, INC.

Exhibit 31.1

CERTIFICATION

I, Hollings C. Renton, Chairman of the Board, President and Chief
Executive Officer of Onyx Pharmaceuticals, Inc., certify that:

1.I have reviewed this Quarterly Report on Form 10-Q of Onyx Pharmaceuticals,
Inc.;

2.Based on my knowledge, this report does not contain any untrue statement of
a material fact or omit to state a material fact necessary to make the
statements made, in light of the circumstances under which such statements were
made, not misleading with respect to the period covered by this report;

3.Based on my knowledge, the financial statements, and other financial
information included in this report, fairly present in all material respects
the financial condition, results of operations and cash flows of the registrant
as of, and for, the periods presented in this report;

4.The registrants other certifying officers and I are responsible for
establishing and maintaining disclosure controls and procedures (as defined in
Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:



| | a) |  | Designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our supervision,
to ensure that material information relating to the registrant,
including its consolidated subsidiaries, is made known to us by others
within those entities, particularly during the period in which this
report is being prepared;         
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| | b) |  | Evaluated the effectiveness of the registrants disclosure controls
and procedures and presented in this report our conclusions about the
effectiveness of the disclosure controls and procedures, as of the end
of the period covered by this report based on such evaluation; and                                                                                                    
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| | c) |  | Disclosed in this report any change in the registrants internal
control over financial reporting that occurred during the registrants
most recent fiscal quarter (the registrants fourth fiscal quarter in
the case of an annual report) that has materially affected, or is
reasonably likely to materially affect, the registrants internal
control over financial reporting; and

5.The registrants other certifying officer(s) and I have disclosed, based on
our most recent evaluation of internal control over financial reporting, to the
registrants auditors and the audit committee of the registrants board of
directors (or persons performing the equivalent functions):



| | a) |  | All significant deficiencies and material weaknesses in the design or
operation of internal control over financial reporting which are
reasonably likely to adversely affect the registrants ability to
record, process, summarize and report financial information; and
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| | b) |  | Any fraud, whether or not material, that involves management or other
employees who have a significant role in the registrants internal
control over financial reporting.                                                                                               

Dated: November 13, 2003

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| |  | /s/ Hollings C. Renton                                                                                                     
| |  |                                                                                                                            
| |  | Hollings C. Renton
Chairman of the Board, President and Chief Executive Officer
(Principal Executive and Financial Officer)

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