FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL OMB Number: 3235-0287 Expires: January 31, 2005 Estimated average burden hours per response... 0.5

(Print or Type Responses)

1. Name and Address of Reporting Person * CONTRAN CORP   2. Issuer Name and Ticker or Trading Symbol KRONOS WORLDWIDE INC [KRO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 5430 LBJ FRWY, SUITE 1700 3. Date of Earliest Transaction (Month/Day/Year) 04/21/2006 (Street) DALLAS, TX 75240 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock $0.01 par value 04/21/2006   J(1)   5,100 A $ 30 28,927,421 I by Valhi (2) Common Stock $0.01 par value 04/21/2006   J(1)   300 A $ 29.88 28,927,721 I by Valhi (2) Common Stock $0.01 par value 04/21/2006   J(1)   100 A $ 29.71 28,927,821 I by Valhi (2) Common Stock $0.01 par value 04/21/2006   J(1)   800 A $ 29.5 28,928,621 I by Valhi (2) Common Stock $0.01 par value 04/24/2006   J(1)   600 A $ 30 28,929,221 I by Valhi (2) Common Stock $0.01 par value               17,516,132 I by NL (3) Common Stock $0.01 par value               5,203 I by TFMC (4)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
	Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.		SEC 1474 (9-02)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
CONTRAN CORP 5430 LBJ FRWY SUITE 1700 DALLAS, TX 75240		X
VALHI INC /DE/ THREE LINCOLN CENTER 5430 LBJ FREEWAY SUITE 1700 DALLAS, TX 75240		X
DIXIE RICE AGRICULTURE CORP INC 600 PASQUIERE ST GUEYDAN, LA 70542		X
SOUTHWEST LOUISIANA LAND CO INC 402 CANAL ST HOUMA, LA 70360		X
TITANIUM METALS CORP TITANIUM METALS CORP 1999 BROADWAY SUITE 4300 DENVER, CO 80202		X
VALHI GROUP INC 5430 LBJ FREEWAY SUITE 1700 DALLAS, TX 75240		X
NL INDUSTRIES INC 5430 LBJ FREEWAY SUITE 1700 DALLAS, TX 75240-2697		X
TIMET FINANCE MANAGEMENT CO 913 N MARKET ST SUITE 217 WILMINGTON, DE 19801		X
VALHI HOLDING CO 5430 LBJ FREEWAY SUITE 1700 DALLAS, TX 75240		X
SIMMONS HAROLD C THREE LINCOLN CENTRE 5430 LBJ FREEWAY STE 1700 DALLAS, TX 75240-2697	X	X	Chairman of the Board & CEO

Signatures

A. Andrew R. Louis, Secretary, for Contran Corporation		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Secretary, for Valhi, Inc.		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Secretary, for Dixie Rice Agricultrual Corpoation, Inc.		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Secretary, for Southwest Louisiana Land Company, Inc.		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Assistant Secretary, for Titanium Metals Corporation		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Secretary, for Valhi Group, Inc.		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Assistant Secretary, for NL Industries, Inc.		04/24/2006
**Signature of Reporting Person		Date
Gregory M. Swalwell, Vice President, for TIMET Finance Management Company		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Secretary, for Valhi Holding Company		04/24/2006
**Signature of Reporting Person		Date
A. Andrew R. Louis, Attorney-in-fact, for Harold C. Simmons		04/24/2006
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Open market purchase by Valhi, Inc. See the Additional Information filed as Exhibit 99 to this statement for a description of the relationships among the persons joining in this filing.
(2)	Directly held by Valhi, Inc. See the Additional Information filed as Exhibit 99 to this statement for a description of the relationships among the persons joining in this filing.
(3)	Directly held by NL Industries, Inc. See the Additional Information filed as Exhibit 99 to this statement for a description of the relationships among the persons joining in this filing.
(4)	Directly held by TIMET Finance Management Company. See the Additional Information filed as Exhibit 99 to this statement for a description of the relationships among the persons joining in this filing.
Remarks: Mr. Harold C. Simmons and his spouse directly hold 4,755 and 36,356 shares, respectively, of the common stock of the issuer.  Mr. Simmons disclaims beneficial ownership of the shares of the issuer's common stock that his spouse owns. This form is also filed on behalf of Dixie Holding Company, 5430 LBJ Freeway, Suite 1700, Dallas, TX 75240 By:  /s/ A. Andrew  R. Louis, Secretary (executed 04/24/2006), National City Lines, Inc., 5430 LBJ Freeway, Suite 1700, Dallas, TX 75240 By:  /s/ A. Andrew R. Louis, Secretary (executed 04/24/2006) NOA, Inc., 5430 LBJ Freeway, Suite 1700, Dallas, TX 75240 By:  /s/  A. Andrew R. Louis, Secretary (executed 04/24/2006) and Tremont LLC, 5430 LBJ Freeway, Suite 1700, Dallas, TX 75240 By:  /s/  A. Andrew R. Louis, Secretary (executed 04/24/2006). See the Additional Information filed as Exhibit 99 to this statement for a description of the relationships among the persons  joining in this filing. Exhibit Index Exhibit 99 - Additional Information

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB number.