As filed with the Securities and Exchange Commission on February 23, 2007.
                                                     Registration No. 333-125982

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                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                         POST-EFFECTIVE AMENDMENT NO. 2
                                   TO FORM S-1
                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                              --------------------

                              CONNETICS CORPORATION
             (Exact name of registrant as specified in its charter)

          Delaware                 3160 Porter Drive           94-3173928
(State or other jurisdiction  Palo Alto, California 94304   (I.R.S. Employer
    of incorporation or              (650) 843-2800       Identification Number)
      organization)

    (Address, including zip code, and telephone number, including area code,
                  of registrant's principal executive offices)


                               Jeffrey S. Thompson
                             Chief Executive Officer
                              CONNETICS CORPORATION
                                3160 Porter Drive
                           Palo Alto, California 94304
                                 (650) 843-2800

                                    Copies to
                               William Grant, Esq.
                          Willkie Farr & Gallagher LLP
                               787 Seventh Avenue
                               New York, NY 10019
                                 (212) 728-8000

            (Name, address, including zip code, and telephone number,
                   including area code, of agent for service)

Approximate date of commencement of proposed sale to public: Not applicable.

If any of the securities being registered on this Form are to be offered on a
delayed or continuous basis pursuant to Rule 415 under the Securities Act, check
the following box. [ ]

If this Form is filed to register additional securities for an offering pursuant
to Rule 462(b) under the Securities Act, check the following box and list the
Securities Act registration statement number of the earlier effective
registration statement for the same offering. [ ]





If this Form is a post-effective amendment filed pursuant to Rule 462(c) under
the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [ ]

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under
the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [ ]





                          DEREGISTRATION OF SECURITIES


A Registration Statement on Form S-1 (Registration No. 333-125982) was
originally filed with the Securities and Exchange Commission (the "Commission")
on June 20, 2005 by the Registrant pursuant to the terms of a Registration
Rights Agreement filed as Exhibit 4.2 to the Registrant's Current Report on Form
8-K filed with the Commission on March 25, 2005. The Registration Statement
concerned the registration for resale by certain selling securityholders named
therein of up to $200,000,000 principal amount of the Registrant's 2.00%
Convertible Senior Notes due March 30, 2015 (the "2015 Notes") and shares of
common stock issuable upon conversion of the 2015 Notes. The Registrant is
filing this Post-Effective Amendment No. 2 to the Registration Statement to
withdraw from registration all unsold 2015 Notes and related common stock
previously registered for resale under the Registration Statement.





                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, the undersigned
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-1 and has duly caused this
Post-Effective Amendment No. 2 to the Registration Statement to be signed on its
behalf by the undersigned, thereunto duly authorized, in the city of Palo Alto,
State of California, on February 23, 2007.


                                   CONNETICS CORPORATION


                                   By:  /s/ Jeffrey S. Thompson
                                        ----------------------------------------
                                        Name:   Jeffrey S. Thompson
                                        Title:  Chief Executive Officer
                                                (Principal Executive Officer)

     Pursuant to the requirements of the Securities Act of 1933, this
Post-Effective Amendment No. 2 to the Registration Statement has been signed on
February 23, 2007 by the following persons in the capacities indicated.


                                        /s/ Jeffrey S. Thompson
                                        ----------------------------------------
                                        Name:   Jeffrey S. Thompson
                                        Title:  Chief Executive Officer
                                                (Principal Executive Officer)


                                        /s/ Michael Cornelius
                                        ----------------------------------------
                                        Name:   Michael Cornelius
                                        Title:  Executive Vice President
                                                (Principal Financial Officer)


                                        /s/ Jeffrey Wadman
                                        ----------------------------------------
                                        Name:   Jeffrey Wadman
                                        Title:  Vice President
                                                (Principal Accounting Officer)


                                        /s/ Charles W. Stiefel
                                        ----------------------------------------
                                        Name:   Charles W. Stiefel
                                        Title:  Director


                                        /s/ Brent Stiefel
                                        ----------------------------------------
                                        Name:   Brent Stiefel
                                        Title:  Director


                                        /s/ Michael Cornelius
                                        ----------------------------------------
                                        Name:   Michael Cornelius
                                        Title:  Director