EXHIBIT 32.1

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO SECTION 906

OF THE SARBANES-OXLEY ACT OF 2002

Pursuant to 18 U.S.C. Section 1350, the undersigned Officer of Opexa Therapeutics, Inc.(the “Company”), hereby certifies, to such officer’s knowledge, that the Company’s Annual Report on Form 10-KSB for the year ended December 31, 2006 (the “Report”) fully complies with the requirements of Section 13(a) or Section 15(d), as applicable, of the Securities Exchange Act of 1934 and that the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

/s/ DAVID B. MCWILLIAMS

David B. McWilliams

President and Chief Executive Officer

Date: March 15, 2007