This filing is made pursuant to
                                             Rule 424(b)(3) under the Securities
                                             Act of 1933 in connection with
                                             Registration No. 333-71896.


       PROSPECTUS SUPPLEMENT NO. 21 TO PROSPECTUS DATED JANUARY 15, 2002 

                  LABORATORY CORPORATION OF AMERICA HOLDINGS

                                $744,000,000
Aggregate Principal Amount at Maturity of Liquid Yield Option(TM) Notes due 2021
                       (Zero Coupon - Subordinated)
                                    and
        Common Stock issuable upon Conversion or Purchase of the LYONs

                 -------------------------------------------

      This prospectus supplement will be used by the holders of LYONs listed 
below to resell their LYONs or the shares of our common stock, par value $0.10 
per share, issuable upon conversion or purchase of the LYONs.

      You should read this prospectus supplement together with the prospectus 
dated January 15, 2002, which is to be delivered with this prospectus 
supplement.

      The table below sets forth additional and updated information concerning 
beneficial ownership of the LYONs, and supplements and, to the extent 
inconsistent with, amends the table appearing under the caption "Selling 
Securityholders" beginning on page 37 of the prospectus.  To the extent that a 
selling securityholder is listed both in the table below and in the table 
appearing in the prospectus, the information set forth below regarding that 
selling securityholder supersedes the information set forth in the prospectus.
We have prepared this table based on information given to us by the selling 
securityholders listed below prior to the date hereof.

                            Aggregate                               Percentage
                            Principal    Percentage    Number of        of
                             Amount          of          Shares        Common 
                           at Maturity      LYONs       of Common      Stock
                            of LYONs    Outstanding   Stock Owned   Outstanding
                           Owned and      Prior to     and that       Prior
                            that May        the         May be        to the
Name                        be Sold       Offering      Sold(1)     Offering(2)
-------------------------- ----------   -----------   ------------  -----------
Saranac Capital Management 
L.P., FBO Citigroup 
Alternative Investments 
Diversified Arbitrage 
Strategies Fund Ltd. (3)    $3,144,000       *           42,163          *

Saranac Capital Management
L.P., FBO GM Welfare 
Benefits Trust (3)              73,000       *              978          *

Saranac Capital Management
L.P., FBO Citigroup 
Alternative Investments 
QIP Multi Strategy 
Arbitrage Portfolio (3)     17,454,000      2.35%       234,072          *

---------------------
*	Less than 1%.


(1)  Assumes conversion of all of the holder's LYONs at a conversion rate of 
     13.4108 shares of common stock per $1,000 principal amount at maturity 
     of the LYONs as a result of a 2-for-1 forward split on May 10, 2002.  
     This conversion rate is subject to adjustment, however, as described 
     under "Description of LYONs-Conversion Rights-Conversion Adjustments and 
     Delivery of Common Stock" beginning on page 16 of the prospectus.  As a 
     result, the number of shares of common stock issuable upon conversion of 
     the LYONs may increase or decrease in the future.

(2)  Calculated based on Rule 13d-3(d)(1)(i) of the Exchange Act using 
     136,394,820 shares of common stock outstanding as of December 28, 2004.  
     In calculating this amount for each holder, we treated as outstanding the 
     number of shares of common stock issuable upon conversion of all of that 
     holder's LYONs, but we did not assume conversion of any other holder's 
     LYONs.

(3)  Previously registered as a selling securityholder under the name of 
     Salomon Smith Barney. The Aggregate Principal Amount represents the 
     remaining assets in this account that were transferred to Saranac Capital 
     Management L.P. as a result of a spin-off. Saranac Capital Management L.P. 
     acts as a discretionary investment advisor and may be deemed to act on the 
     behalf of the beneficial owner of such debentures.
 
                -------------------------------------------

     Investing in the LYONs involves risks that are described in "Risk Factors 
Relating to the LYONs" beginning on page 8 of the prospectus.

     Neither the Securities and Exchange Commission nor any state securities 
commission has approved or disapproved these securities, or determined if this 
prospectus is truthful or complete.  Any representation to the contrary is a 
criminal offense.

        The date of this prospectus supplement is December 30, 2004

(TM)Trademark of Merrill Lynch & Co., Inc.