Exhibit 32.1

    CERTIFICATION OF CHIEF EXECUTIVE OFFICER PURSUANT TO 18 U.S.C. 'SS' 1350,
      AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     Pursuant to 18 U.S.C. 'SS' 1350, the undersigned certifies that, to the
best of my knowledge, the Quarterly Report on Form 10-Q for the period ended
September 30, 2004 of Quest Diagnostics Incorporated, as being filed with the
Securities and Exchange Commission concurrently herewith, fully complies with
the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of
1934 (15 U.S.C. 'SS' 78m or 78o(d)) and that the information contained in the
Quarterly Report fairly presents, in all material respects, the financial
condition and results of operations of Quest Diagnostics Incorporated.


Dated: October 29, 2004                 /s/ Surya N. Mohapatra
                                        ----------------------------------------
                                            Surya N. Mohapatra, Ph.D.
                                            President and
                                            Chief Executive Officer