Michael E. Tenta
(650) 843-5636
mtenta@cooley.com VIA EDGAR

August 24, 2010

Securities and Exchange Commission

Attention:  Jim B. Rosenberg
Joel Parker
Vanessa Robertson
Suzanne Hayes
Karen Ubell

100 F Street, N.E.
Washington, D.C. 20549

Re:   Onyx Pharmaceuticals, Inc.
Form 10-K for Fiscal Year Ended December 31, 2009
Filed February 23, 2010
Definitive Proxy Statement filed April 9, 2010
File No. 000-28928

Ladies and Gentlemen:

     On behalf of Onyx Pharmaceuticals, Inc. (the “Company”), this letter is being submitted in response to comments received from the staff of the Commission (the “Staff”) by letter dated August 17, 2010, with respect to the Company’s Form 10-K for Fiscal Year Ended December 31, 2009 and Definitive Proxy Statement filed April 9, 2010.

     Please be advised that the Company currently expects that it will provide its response to the Staff’s comment letter on or before September 15, 2010 and will further advise the Staff if it becomes unable to do so.

     Please do not hesitate to contact me at (650) 843-5636 if you have any questions or would like any additional information regarding this matter.

Sincerely,
 

/s/ Michael E. Tenta  

Michael E. Tenta 

cc:   Matthew K. Fust
Executive Vice President and Chief Financial Officer