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 of NL  Industries,  Inc. (the Company) on
Form 10-K for the year ended  December 31, 2004 as filed with the Securities and
Exchange Commission on the date hereof (the Report), I, Harold C. Simmons, Chief
Executive  Officer of the Company,  and I, Gregory M. Swalwell,  Chief Financial
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/ Harold C. Simmons
---------------------------
Harold C. Simmons
   Chief Executive Officer


/s/ Gregory M. Swalwell
---------------------------
Gregory M. Swalwell
   Chief Financial Officer


March 30, 2005


Note: The certification  the registrant  furnishes in this exhibit is not deemed
"filed" for purposes of Section 18 of the  Securities  Exchange Act of 1934,  as
amended,  or otherwise subject to the liabilities of that Section.  Registration
Statements or other documents filed with the Securities and Exchange  Commission
shall not incorporate this exhibit by reference,  except as otherwise  expressly
stated in such filing.