<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM ONYX
PHARMACEUTICALS, INC.'S UNAUDITED CONDENSED BALANCE SHEET DATED SEPTEMBER 30,
1999, AND UNAUDITED CONDENSED STATEMENT OF OPERATIONS FOR THE NINE MONTHS ENDED
SEPTEMBER 30, 1999, AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000

                             
<PERIOD-TYPE>                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1999
<PERIOD-START>                             JAN-01-1999
<PERIOD-END>                               SEP-30-1999
<CASH>                                          11,780
<SECURITIES>                                     3,061
<RECEIVABLES>                                        0
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                                15,546
<PP&E>                                          12,360
<DEPRECIATION>                                   9,197
<TOTAL-ASSETS>                                  19,168
<CURRENT-LIABILITIES>                            9,558
<BONDS>                                          2,931
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                            12
<OTHER-SE>                                       8,866
<TOTAL-LIABILITY-AND-EQUITY>                    19,168
<SALES>                                              0
<TOTAL-REVENUES>                                 6,723
<CGS>                                                0
<TOTAL-COSTS>                                   20,549
<OTHER-EXPENSES>                                     0
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                 253
<INCOME-PRETAX>                               (13,155)
<INCOME-TAX>                                         0
<INCOME-CONTINUING>                           (13,155)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                  (13,155)
<EPS-BASIC>                                     (1.14)
<EPS-DILUTED>                                   (1.14)