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

In connection with the Quarterly Report of Cass Information Systems, Inc. ("the
Company") on Form 10-Q for the period ended June 30, 2007 as filed with the
Securities and Exchange Commission on the date hereof (the "Report"), I,
Lawrence A. Collett, Chairman and Chief Executive Officer of the Company,
certify, pursuant to 18 U.S.C. ss. 1350, as adopted pursuant to ss. 906 of the
Sarbanes-Oxley Act of 2002, that:

     (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/ Lawrence A. Collett
                                    --------------------------------------------
                                    Lawrence A. Collett
                                    Chairman and Chief Executive Officer
                                    (Principal Executive Officer)
                                    August 6, 2007


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

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