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                                                                    EXHIBIT 5.1
 
                      [DAVIS POLK & WARDWELL LETTERHEAD]
 
                                 212-450-4000
 
                                          May 6, 1997
 
Laboratory Corporation of America Holdings
358 South Main Street
Burlington, North Carolina 27215
 
Ladies and Gentlemen:
 
  We have acted as counsel to Laboratory Corporation of America Holdings, a
Delaware corporation (the "Company") in connection with the Company's
Registration Statement on Form S-3 (the "Registration Statement") filed with
the Securities and Exchange Commission pursuant to the Securities Act of 1933,
as amended, for the registration of the Company's (i) transferable
subscription rights (the "Rights"); (ii) Series A Convertible Exchangeable
Preferred Stock, par value $0.10 per share (the "Series A Exchangeable
Preferred Stock") and Series B Convertible Pay-in-Kind Preferred Stock, par
value $0.10 per share, with an aggregate liquidation preference of
$828,200,000 (the "Series B PIK Preferred Stock" and, together with the Series
A Exchangeable Preferred Stock, the "Preferred Stock"); (iii) $250,562,450
aggregate principal amount of convertible subordinated notes due 2012 (the
"Notes") which may be issued in exchange for the Preferred Stock; and (iv)
such currently indeterminate number of shares of Common Stock, par value $0.01
per share (the "Common Stock") as may be issuable upon conversion of the
Preferred Stock and the Notes. The Notes are to be issued pursuant to an
Indenture (the "Indenture") between the Company and First Union National Bank
of North Carolina, as Trustee (the "Trustee").
 
  We have examined originals or copies, certified or otherwise identified to
our satisfaction, of such documents, corporate records, certificates of public
officials and other instruments as we have deemed necessary or advisable for
the purposes of rendering this opinion.
 
  On the basis of the foregoing, we are of the opinion that:
 
  (i) The Rights when duly authorized and issued in accordance with the terms
      of the Rights Offering (as defined in the Registration Statement) will
      be validly issued;
 
  (ii) Upon the designation of the relative rights, preferences and
       limitations of the Preferred Stock by the Board of Directors and the
       proper filing with the Secretary of State of the State of Delaware of
       the Certificate of Designation relating to each series of the
       Preferred Stock, when the Preferred Stock has been duly authorized,
       issued and paid for in accordance with the terms of the Rights
       Offering or issued in respect of the dividend requirements of the
       Series B PIK Preferred Stock, as the case may be, the Preferred Stock
       will be validly issued, fully-paid and non-assessable, and the
       issuance of such Preferred Stock will not be subject to any preemptive
       rights;
 
  (iii) When the Indenture to be entered into in connection with the issuance
        of the Notes has been duly authorized, executed and delivered by the
        Trustee and the Company and the Notes have been duly authorized,
        executed, authenticated, issued and delivered in exchange for the
        Series A Exchangeable Preferred Stock in accordance with the terms of
        the Series A Exchangeable Preferred Stock and the Indenture, the
        Notes will constitute valid and binding obligations of the Company
        enforceable in accordance with their terms, except as (a) the
        enforceability thereof may be limited by bankruptcy, insolvency,
        reorganization, fraudulent transfer, moratorium or similar laws now
        or hereinafter in effect relating to or affecting the enforcement of
        creditors' rights generally and (b) the availability of equitable
        remedies may be limited by equitable principles of general
        applicability (regardless of whether considered in a proceeding at
        law or in equity); and
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    Laboratory
  Corporation of
 America Holdings
                                                                    May 6, 1997
  (iv) When any shares of Common Stock are issued upon conversion of any
       shares of Preferred Stock or any Notes, as the case may be, such
       shares of Common Stock will be duly authorized, validly issued, fully-
       paid and non-assessable and the issuance of such Common Stock will not
       be subject to any preemptive rights.
 
  In connection with the opinions expressed above, we have assumed that, at or
prior to the time of the delivery of any such security, (i) the Board of
Directors shall have duly established the terms of such security and duly
authorized the issuance and sale of such security and such authorization shall
not have been modified or rescinded and that prior to the issuance of Series B
PIK Preferred Stock in the form of dividends, the Board of Directors and
stockholders of the Company shall have approved an increase in the authorized
share capital of the Company sufficient to authorize such issuance and all
required filings with the Secretary of State of Delaware in connection
therewith shall have been made; (ii) in the case of the Common Stock, the
Board of Directors and stockholders of the Company shall have approved an
increase in the authorized share capital of the Company sufficient to enable
all Preferred Stock and/or Notes to be converted and all required filings with
the Secretary of State of Delaware in connection therewith shall have been
made; and (iii) there shall not have occurred any change in law affecting the
validity or enforceability of such security. We have also assumed that neither
the issuance and delivery of any security to be issued and delivered
subsequent to the date hereof, nor the compliance by the Company with the
terms of such security will violate any applicable law or will result in a
violation of any provision of any instrument or agreement then binding upon
the Company, or any restriction imposed by any court or governmental body
having jurisdiction over the Company.
 
  We are members of the Bar of the State of New York and the foregoing opinion
is limited to the laws of the State of New York, the federal laws of the
United States of America and the General Corporation Law of the State of
Delaware.
 
  We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement. In addition, we consent to the reference to us under
the caption "Legal Matters" in the prospectus.
 
  This opinion is rendered to you solely in connection with the above matter.
This opinion may not be relied upon by you for any other purpose or relied
upon by or furnished to any other person without our prior written consent.
 
                                          Very truly yours,
 
                                          /s/  Davis Polk & Wardwell
 
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