EXHIBIT 2


                             JOINT FILING AGREEMENT

     In accordance with Rule 13d-1(k)  promulgated under the Securities Exchange
Act of 1934,  the  undersigned  agree to the  joint  filing  of a  Statement  on
Schedule 13D  (including  any and all  amendments  thereto)  with respect to the
shares of Vysis,  Inc. and further  agree to the filing of this  agreement as an
Exhibit thereto. In addition,  each party to this Agreement expressly authorizes
each other party to this  Agreement to file on its behalf any and all amendments
to such Statement on Schedule 13D.

Date:  October 25, 2001

BP p.l.c.

By:     /s/ Lesley Stockwell
        ----------------------
Name:   L. J. Stockwell
Title:  Assistant Company
        Secretary


BP America Inc.

By:     /s/ D. B. Pinkert
        -------------------------
Name:   D. B. Pinkert
Title:  Corporate Secretary


BP Corporation North America
Inc.

By:     /s/ D. B. Pinkert
        -------------------------
Name:   D. B. Pinkert
Title:  Corporate Secretary


Amoco Technology Company

By:     /s/ D. B. Pinkert
        -------------------------
Name:   D. B. Pinkert
Title:  Vice President