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 Annual Report of NL  Industries,  Inc. (the Company) on
Form 10-K for the year ending December 31, 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

March 12, 2003