EXHIBIT 1 --------- JOINT FILING AGREEMENT In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, each of the persons named below agrees to the joint filing of a Statement on Schedule 13D (including amendments thereto)...

                                                                       EXHIBIT 1
                                                                       ---------
                             JOINT FILING AGREEMENT

In accordance  with Rule 13d-1(k) under the Securities  Exchange Act of 1934, as
amended,  each of the  persons  named  below  agrees  to the  joint  filing of a
Statement on Schedule 13D  (including  amendments  thereto)  with respect to the
common stock,  par value $0.001 per share,  of Idenix  Pharmaceuticals,  Inc., a
Delaware corporation.


Date: November 2, 2005

                                             NOVARTIS AG


                                             By: /s/ Xxxxx Xxxxxxxxx
                                                --------------------------------
                                                Name: Xxxxx Xxxxxxxxx
                                                Title: Authorized Signatory


                                             By: /s/ Xxxxxx Xxxxxxxxxxxx
                                                --------------------------------
                                                Name: Xxxxxx Xxxxxxxxxxxx
                                                Title: Authorized Signatory


                                             NOVARTIS PHARMA AG


                                             By: /s/ Xxxxxxxx Xxxxx
                                                --------------------------------
                                                Name: Xxxxxxxx Xxxxx
                                                Title: Head of Legal Ophtha and
                                                       Oncology Europe

                                             By: /s/  Xxxxxx Xxxxx
                                                --------------------------------
                                                Name: Xxxxxx Xxxxx
                                                Title: Head Operational Treasury



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