EXHIBIT 5.1

      OPINION OF WILSON SONSINI GOODRICH & ROSATI, PROFESSIONAL CORPORATION


                                                                     May 4, 2004

Cytokinetics, Incorporated
280 East Grand Avenue
South San Francisco, CA 94080

         RE:  REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

      We have examined the Registration Statement on Form S-8 to be filed by you
with the Securities and Exchange Commission on May 4, 2004 (the "Registration
Statement"), in connection with the registration under the Securities Act of
1933, as amended, of 4,360,007 shares of your Common Stock, par value $0.001 per
share (the "Shares"), (i) 2,260,007 shares of which are subject to currently
outstanding options under the 1997 Stock Option/Stock Issuance Plan, (ii)
1,454,500 shares of which are to be issued pursuant to options under the 2004
Equity Incentive Plan (iii) 145,500 shares of which are subject to currently
outstanding options under the 2004 Equity Incentive Plan and (iv) 500,000
shares of which are to be issued pursuant to the 2004 Employee Stock Purchase
Plan (collectively, the "Plans"). As your counsel in connection with this
transaction, we have examined the proceedings taken and are familiar with the
proceedings proposed to be taken by you in connection with the issuance and sale
of the Shares pursuant to the Plans.

      It is our opinion that, when issued and sold in the manner described in
the Plans and pursuant to the agreements which accompany each grant under the
Plans, the Shares will be legally and validly issued, fully-paid and
non-assessable.

      We consent to the use of this opinion as an exhibit to the Registration
Statement, and further consent to the use of our name wherever appearing in the
Registration Statement and any amendments thereto.

                                            Very truly yours,

                                            WILSON SONSINI GOODRICH & ROSATI


                                            /s/ Wilson Sonsini Goodrich & Rosati