EXHIBIT 10.1

AMENDMENT NO. 1 TO THIRD AMENDED AND RESTATED CREDIT AND
SECURITY AGREEMENT

                    THIS AMENDMENT NO. 1 TO THIRD AMENDED AND RESTATED CREDIT
AND SECURITY AGREEMENT (this “Amendment”) is entered into as of April 18, 2006,
by and among:

          (1)     QUEST DIAGNOSTICS RECEIVABLES INC., a Delaware corporation
(the “Borrower”),

          (2)     QUEST DIAGNOSTICS INCORPORATED, a Delaware corporation as
initial servicer (together with the Borrower, the “Loan Parties”),

          (3)     VARIABLE FUNDING CAPITAL COMPANY LLC, a Delaware limited
liability company as assignee of Blue Ridge Asset Funding Corporation (“VFCC”),
and WACHOVIA BANK, NATIONAL ASSOCIATION, in its capacity as a Liquidity Bank to
VFCC (together with VFCC, the VFCC Group”),

          (4)     ATLANTIC ASSET SECURITIZATION LLC, a Delaware limited
liability company formerly known as Atlantic Asset Securitization Corp.
(together with its successors, “Atlantic” and together with VFCC, the
“Conduits”), and CALYON NEW YORK BRANCH, in its capacity as a Liquidity Bank to
Atlantic (together with Atlantic, the “Atlantic Group”),

          (5)     WACHOVIA BANK, NATIONAL ASSOCIATION, in its capacity as agent
for the VFCC Group, and CALYON NEW YORK BRANCH, in its capacity as agent for the
Atlantic Group (in such latter capacity, together with its successors in such
latter capacity, the “Atlantic Agent” or a “Co-Agent”), and

          (6)     WACHOVIA BANK, NATIONAL ASSOCIATION, as administrative agent
for the VFCC Group, the Atlantic Group and the Co-Agents (in such capacity,
together with any successors thereto in such capacity, the “Administrative
Agent” and together with each of the Co-Agents, the “Agents”),

with respect to that certain Third Amended and Restated Credit and Security
Agreement dated as of April 20, 2004, by and among the parties hereto (as
heretofore amended, the “Existing Agreement” which, as amended hereby, is
hereinafter referred to as the “Agreement”). 
    

                   Unless otherwise indicated, capitalized terms used in this
Amendment are used with the meanings attributed thereto in the Existing
Agreement.     

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W I T N E S S E T H :

          WHEREAS, on December 1, 2005, Blue Ridge Asset Funding Corporation
assigned all of its right, title and interest in, to any under the Existing
Agreement and other Transaction documents to VFCC; and

          WHEREAS, Atlantic Asset Securitization Corp. underwent a conversion in
status to a limited liability company known as Atlantic Asset Securitization LLC
pursuant to Delaware law; and

          WHEREAS, the parties hereto desire to amend the Existing Agreement as
hereinafter set forth;

          NOW, THEREFORE, in consideration of the premises and the mutual
agreements herein contained, the parties hereto hereby agree as follows:

          1.        Amendments to Existing Agreement.     Subject to the terms
and conditions hereinafter set forth, the parties hereby agree to amend the
Existing Agreement as follows:

          1.1.     All references in the Existing Agreement to “Blue Ridge”
(whether alone or as part of another defined term) or to “Blue Ridge Asset
Funding Corporation” are hereby replaced with “VFCC” and “Variable Funding
Capital Company LLC,” respectively.     

          1.2.     All references in the Existing Agreement to “Atlantic Asset
Securitization Corp.” are hereby replaced with “Atlantic Asset Securitization
LLC.”

          1.3.     Sections 10.1(h) of the Existing Agreement is hereby amended
and restated in its entirety to read as follows:

          (h)       The three-calendar month rolling average Delinquency Ratio
at any Cut-Off Date exceeds 9.00%.     

          2.         Representations.     

          2.1.     Each of the Loan Parties represents and warrants to the
Lenders and the Agents that it has duly authorized, executed and delivered this
Amendment and that the Agreement constitutes, a legal, valid and binding
obligation of such Loan Party, enforceable in accordance with its terms (except
as enforceability may be limited by applicable bankruptcy, insolvency, or
similar laws affecting the enforcement of creditors’ rights generally or by
equitable principles relating to enforceability).     

          2.2.     Each of the Loan Parties further represents and warrants to
the Lenders and the Agents that each of its representations and warranties set
forth in Section 6.1 of the Agreement is true and correct as of the date hereof
and that no Event of Default or Unmatured Default exists as of the date hereof
and is continuing.     

          3.        Conditions Precedent.     This Amendment shall become
effective as of the date first above written upon (a) receipt by the
Administrative Agent of a counterpart hereof duly

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executed by each of the parties hereto, (b) receipt by the VFCC Agent of a
fully-earned and non-refundable extension fee in the amount of $20,000 in
immediately available funds and of an amended and restated VFCC Fee Letter, duly
executed by the parties thereto, and (c) receipt by the Atlantic Agent of a
fully-earned and non-refundable extension fee in the amount of $10,000 in
immediately available funds and of an amended and restated Atlantic Fee Letter,
duly executed by the parties thereto.     

          4.        Miscellaneous.     

          4.1.     Except as expressly amended hereby, the Existing Agreement
and shall remain unaltered and in full force and effect, and each of the parties
hereby ratifies and confirms the Agreement and each of the other Transaction
Documents to which it is a party.     

          4.2.     THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED IN
ACCORDANCE WITH, THE INTERNAL LAWS OF THE STATE OF NEW YORK WITHOUT REFERENCE TO
PRINCIPLES OF CONFLICTS OF LAW.     

          4.3.     EACH LOAN PARTY HEREBY ACKNOWLEDGES AND AGREES THAT:

          4.3.1.  IT IRREVOCABLY (i) SUBMITS TO THE NON-EXCLUSIVE JURISDICTION,
FIRST, OF ANY UNITED STATES FEDERAL COURT, AND SECOND, IF FEDERAL JURISDICTION
IS NOT AVAILABLE, OF ANY NEW YORK STATE COURT, IN EITHER CASE SITTING IN NEW
YORK COUNTY, NEW YORK, IN ANY ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO
THE AGREEMENT, AND (ii) WAIVES, TO THE FULLEST EXTENT IT MAY EFFECTIVELY DO SO,
THE DEFENSE OF AN INCONVENIENT FORUM TO THE MAINTENANCE OF AN ACTION OR
PROCEEDING IN SUCH COURTS.     

          4.3.2.  TO THE EXTENT THAT IT HAS OR HEREAFTER MAY ACQUIRE ANY
IMMUNITY FROM THE JURISDICTION OF ANY COURT OR FROM ANY LEGAL PROCESS (WHETHER
THROUGH SERVICE OR NOTICE, ATTACHMENT PRIOR TO JUDGMENT, ATTACHMENT IN AID TO
EXECUTION, EXECUTION OR OTHERWISE) WITH RESPECT TO ITSELF OR ITS PROPERTY, IT
HEREBY IRREVOCABLY WAIVES SUCH IMMUNITY IN RESPECT OF ITS OBLIGATIONS UNDER OR
IN CONNECTION WITH THE AGREEMENT.     

          4.4.     This Amendment may be executed in any number of counterparts
and by the different parties hereto in separate counterparts, each of which when
so executed shall be deemed to be an original and all of which when taken
together shall constitute one and the same Amendment.     

<Signature pages follow>

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                    IN WITNESS WHEREOF, the parties hereto have executed this
Amendment as of the date first above written.     

  QUEST DIAGNOSTICS RECEIVABLES INC.            By:  /s/      Joseph P. Manory  
  Name: Joseph P. Manory     Title:    Vice President & Treasurer            
QUEST DIAGNOSTICS INCORPORATED       By:  /s/      Joseph P. Manory     Name:
Joseph P. Manory     Title:    Vice President & Treasurer             WACHOVIA
BANK, NATIONAL ASSOCIATION,   INDIVIDUALLY, AS ADMINISTRATIVE AGENT AND AS VFCC
AGENT       By:  /s/      Elizabeth R. Wagner     Name: Elizabeth R. Wagner    
Title:    Managing Director       VARIABLE FUNDING CAPITAL COMPANY LLC     BY:
WACHOVIA CAPITAL MARKETS, LLC, ITS ATTORNEY-IN-FACT     By:  /s/      Douglas R.
Wilson, Jr.     Name: Douglas R. Wilson, Sr.          Title:    Vice President  
    ATLANTIC ASSET SECURITIZATION LLC     By: CALYON NEW YORK BRANCH         AS
ATTORNEY-IN-FACT       By: /s/       Anthony Brown     Name: Anthony Brown    
Title:    Vice President

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  By:  /s/      Tina Kourmpetis     Name: Tina Kourmpetis     Title:    Managing
Director                         CALYON NEW YORK BRANCH, INDIVIDUALLY AND AS
ATLANTIC   AGENT     By:  /s/      Anthony Brown     Name: Anthony Brown    
Title:    Vice President                         By:  /s/      Tina Kourmpetis  
  Name: Tina Kourmpetis     Title:    Managing Director                        
 

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