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                                                                     Exhibit 5.1


                             Morrison & Foerster LLP
                               5200 Republic Plaza
                             370 Seventeenth Street
                           Denver, Colorado 80202-5638


                                  June 29, 2001



Connetics Corporation
3400 West Bayshore Road
Palo Alto, CA  94303

         Re: Registration Statement on Form S-3

Ladies and Gentlemen:

     We have acted as your counsel in connection with the Registration
Statement on Form S-3, File No. 333-45002 (the "Registration Statement") filed
by you with the Securities and Exchange Commission relating to the registration
under the Securities Act of 1933 of 84,511 shares of your common stock, $.001
par value per share (the "Shares").

     In connection therewith, we have reviewed the Registration Statement and
certain of your corporate records, documents, instruments and proceedings taken
in connection with the authorization and issuance of the Shares, and such other
factual and legal matters as we have deemed necessary for purposes of rendering
the opinion set forth herein.

     We have assumed the genuineness of the signatures on and the authenticity
of all documents submitted to us as originals and the conformity to original
documents submitted to us as certified or photostatic copies. We also have
relied upon the accuracy, as to matters of fact, of your officers. We have
relied on your records and have assumed the accuracy and completeness thereof.

     Based upon and subject to the foregoing, we are of the opinion that the
Shares, when issued and sold in the manner described in the Registration
Statement, will be validly issued, fully paid and nonassessable.

     We express no opinion as to matters governed by laws of any jurisdiction
other than the laws of the General Corporation Law of the State of Delaware and
the federal laws of the United States of America, as in effect on the date
hereof.

     We hereby consent to the filing of this opinion with the Securities and
Exchange Commission as an exhibit to the Registration Statement.



                                        Very truly yours,

                                        /s/ Morrison & Foerster LLP