Incara Pharmaceuticals 10-Q 2003 Q2 Quarterly report

EXHIBIT 99.1

CERTIFICATION 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 Incara Pharmaceuticals Corporation (the “Company”) for the period ended March 31, 2003 as filed with the Securities and Exchange Commission on or about the date hereof (the “Report”), I, Clayton I. Duncan, President and Chief Executive Officer, hereby certify, pursuant to 18 U.S.C. 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to my knowledge:

(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/    CLAYTON I. DUNCAN      

Clayton I. Duncan

President and Chief Executive Officer

May 8, 2003