AGREEMENT

                                                                       EXHIBIT 4

                                    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
relating to the Common Stock, $0.001 par value, of Seattle Genetics, Inc. is
being filed with the Securities and Exchange Commission on behalf of each of
them.

August 15, 2006

                                                     By:  /s/ ▇▇▇▇▇▇ ▇. ▇▇▇▇▇
                                                          ----------------------
                                                          ▇▇▇▇▇▇ ▇. ▇▇▇▇▇

                                                     By:  /s/ ▇▇▇▇▇ ▇. ▇▇▇▇▇
                                                          ----------------------
                                                          ▇▇▇▇▇ ▇. ▇▇▇▇▇



                                Page 7 of 7 Pages