EXHIBIT 99.1



      CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER
                                   PURSUANT TO
                             18 U.S.C. SECTION 1350,
      AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002



I, Gerald J. Burnett, certify, pursuant to 18 U.S.C. Section 1350, as adopted
pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly
Report of Avistar Communications Corporation on Form 10-Q for the fiscal quarter
ended September 30, 2002 fully complies with the requirements of Section 13(a)
or 15(d) of the Securities Exchange Act of 1934 and that information contained
in such Quarterly Report on Form 10-Q fairly presents in all material respects
the financial condition and results of operations of Avistar Communications
Corporation.

                                             By:     /s/ GERALD J. BURNETT
                                                    ----------------------------
                                             Name:  Gerald J. Burnett
                                             Title: Chief Executive Officer

I, Robert J. Habig, certify, pursuant to 18 U.S.C. Section 1350, as adopted
pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly
Report of Avistar Communications Corporation on Form 10-Q for the fiscal quarter
ended September 30, 2002 fully complies with the requirements of Section 13(a)
or 15(d) of the Securities Exchange Act of 1934 and that information contained
in such Quarterly Report on Form 10-Q fairly presents in all material respects
the financial condition and results of operations of Avistar Communications
Corporation.

                                             By:    /s/ ROBERT J. HABIG
                                                    ----------------------------
                                             Name:  Robert J. Habig
                                             Title: Chief Financial Officer