Marsh & McLennan Companies (MMC) 10-Q 2007 Q1 Quarterly report

Exhibit 32.1

Certification of Chief Executive Officer and Chief Financial Officer

The certification set forth below is being submitted in connection with the Quarterly Report on Form 10-Q for the fiscal quarter ended March 31, 2007 of Marsh & McLennan Companies, Inc. (the “Report”) for the purpose of complying with Rule 13a-14(b) or Rule 15d-14(b) under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and Section 1350 of Chapter 63 of Title 18 of the United States Code.

Michael G. Cherkasky, the President and Chief Executive Officer, and Matthew B. Bartley, the Chief Financial Officer, of Marsh & McLennan Companies, Inc. each certifies that, to the best of his knowledge:

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

2. the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of Marsh & McLennan Companies, Inc.

Date: May 10, 2007/s/ Michael G. Cherkasky

Michael G. Cherkasky

President and Chief Executive Officer

Date: May 10, 2007/s/ Matthew B. Bartley

Matthew B. Bartley

Chief Financial Officer