Exhibit 99.1


                            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 NL Industries, Inc. (the Company) on
Form 10-Q for the period ending September 30, 2002 as filed with the Securities
and Exchange Commission on the date hereof (the Report), I, J. Landis Martin,
Chief Executive Officer of the Company, certify, pursuant to 18 U.S.C. Section
1350, as adopted pursuant to Section 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/   J. Landis Martin
- ------------------------------------
   J. Landis Martin
     Chief Executive Officer

November 12, 2002