Exhibit 99.1

                    Certification of CEO and CFO Pursuant to
                             18 U.S.C. Section 1350,
                             as Adopted Pursuant to
                  Section 906 of the Sarbanes-Oxley Act of 2002

         In connection with the Quarterly Report on Form 10-Q of ISP Chemco Inc.
(the "Company") for the quarterly period ended March 30, 2003 as filed with the
Securities and Exchange Commission on the date hereof (the "Report"), Sunil
Kumar, as President and Chief Executive Officer of the Company, and Neal E.
Murphy, as Senior Vice President and Chief Financial Officer of the Company,
each hereby certifies, pursuant to 18 U.S.C. Section 1350, as adopted pursuant
to Section 906 of the Sarbanes-Oxley Act of 2002, that, to the best of his
knowledge and belief:

         (1) The Report fully complies with the requirements of Section 13(a) or
15(d) of the Securities Exchange Act of 1934; and

         (2) The information contained in the Report fairly presents, in all
material respects, the financial condition and results of operations of the
Company.


 /s/ Sunil Kumar
- ---------------------------------
Name:   Sunil Kumar
Title:  President and Chief Executive Officer

Date:   May 13, 2003


  /s/ Neal E. Murphy
- ---------------------------------
Name:   Neal E. Murphy
Title:  Senior Vice President and
          Chief Financial Officer

Date:   May 13, 2003

A signed original of this written statement required by Section 906 has been
provided to ISP Chemco Inc. and will be retained by ISP Chemco Inc. and
furnished to the Securities and Exchange Commission or its staff upon request.

This certification accompanies the Report pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002 and shall not, except to the extent required by the
Sarbanes-Oxley Act of 2002, be deemed filed by the Company for purposes of
Section 18 of the Securities Exchange Act of 1934, as amended.