AGREEMENT

                                                                   EXHIBIT 10.12

                     THIRD AMENDMENT TO CONSULTING AGREEMENT

THIS THIRD AMENDMENT TO Consulting agreement ("THIRD AMENDMENT") is entered into
and made effective as of December 31, 2003 ("THIRD AMENDMENT EFFECTIVE DATE") by
and between Connetics Corporation ("CONNETICS") and Xxxxxx X. Xxxxx, M.D. ("XX.
XXXXX"). Unless otherwise indicated, a capitalized term within this Third
Amendment shall have the same meaning as the same capitalized term within the
Initial Agreement (defined below).

                                    AGREEMENT

Connetics and Xx. Xxxxx are Parties to a Consulting Agreement dated January 1,
2002 ("INITIAL AGREEMENT"), to an Amendment to Consulting Agreement dated
December 11, 2002 ("AMENDMENT") and to a Second Amendment to Consulting
Agreement dated January 1, 2003 ("SECOND AMENDMENT"). The Initial Agreement, the
Amendment and the Second Amendment are to be known collectively as the
"CONSULTING AGREEMENT." Connetics and Xx. Xxxxx desire to amend the terms of the
Consulting Agreement as set forth below.

1.   Section 2(a) of the Consulting Agreement is superceded and replaced, in its
     entirety, to read as follows:

          2(a) Connetics hereby retains Xx. Xxxxx and Xx. Xxxxx hereby accepts
               this retainer as a consultant to Connetics for the term
               commencing on January 1, 2002 and ending on December 31, 2004.

2.   This Third Amendment may be executed in a number of identical counterparts,
     each of which will be deemed an original, but all of which together will
     constitute one and the same instrument.

3.   All of the remaining provisions of the Consulting Agreement shall continue
     in full force and effect as though fully set forth in this Third Amendment.

IN WITNESS WHEREOF, the Parties have entered into this Third Amendment as of the
Third Amendment Effective Date.

     "CONNETICS"                                    "XX. XXXXX"
  CONNETICS CORPORATION                           XXXXXX X. XXXXX



Signature: /s/ Xxxxxx X. Xxxxxxx          Signature: /s/ Xxxxxx X. Xxxxx
           ------------------------                  -----------------------
Print: Xxxxxx X. Xxxxxxx                  Print: Xxxxxx X. Xxxxx, M.D.
Title: President and Chief                Social Security No:  ____________
       Executive Officer