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 Annual Report on Form 10-K of Kronos Incorporated (the “Company”) for the fiscal year ended September 30, 2006 as filed with the Securities and Exchange Commission on the date hereof (the “Report”), the undersigned, Paul A. Lacy, President and Principal Executive Officer of the Company, and Mark V. Julien, Chief Financial Officer of the Company, each hereby certifies, pursuant to 18 U.S.C. Section 1350, 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.

Date: December 13, 2006 /S/    PAUL A. LACY Paul A. Lacy President

Date: December 13, 2006 /S/    MARK V. JULIEN Mark V. Julien Chief Financial Officer and Treasurer