JOINT FILING AGREEMENT

                                                                    EXHIBIT 99.3

                            JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k)(1) under the Securities Exchange Act of 1934,
as amended, the undersigned hereby agree that this Statement on Schedule 13D
with respect to the beneficial ownership of shares of Common Stock of Chiron
Corporation is filed jointly, on behalf of each of them. This Agreement may be
executed in any number of counterparts, all of which taken together shall
constitute one and the same instrument.

Dated:  October 31, 2005

                                       NOVARTIS BIOTECH
                                       PARTNERSHIP, INC.


                                       By:    /s/ Xxxxx X. Xxxxxxxxx
                                           --------------------------
                                           Name:  Xxxxx X. Xxxxxxxxx
                                           Title: Vice President


                                       NOVARTIS CORPORATION


                                       By:    /s/ Xxxx Xxxxxxxx
                                           ---------------------------
                                           Name:  Xxxx Xxxxxxxx
                                           Title: Vice President


                                       NOVARTIS PHARMA AG


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

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


                                       NOVARTIS AG


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