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 ended March 31, 2003 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

May 9, 2003

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