EXHIBIT 10.33

FOURTH AMENDMENT TO CREDIT AGREEMENT

THIS FOURTH AMENDMENT TO CREDIT AGREEMENT (this "Fourth Amendment") is entered into as of November 13, 2000 among Covance Inc. (the "Borrower"),
certain of the Borrower's Subsidiaries (individually a "Guarantor" and collectively the "Guarantors"), the Lenders party to the Credit Agreement defined below (the "Lenders"), Bank of America, N.A.,
formerly NationsBank, N.A., as Administrative Agent (the "Administrative Agent") and Wachovia Bank, N.A., successor by merger to Wachovia Bank of Georgia, N.A., as Syndication Agent (the "Syndication
Agent"; the Administrative Agent, together with the Syndication Agent, may be referred to herein as the "Agents"). Capitalized terms used herein and not otherwise defined herein have the respective
meanings given to them in the Credit Agreement.

RECITALS

WHEREAS, the Borrower, the Guarantors, the Lenders, the Administrative Agent and the Syndication Agent are parties to a Credit Agreement dated as of
November 26, 1996 (as previously amended and as further amended, modified, supplemented or restated from time to time, the "Credit Agreement");

WHEREAS,
the Borrower has requested that the Lenders consent to an amendment of certain provisions of the Credit Agreement; and

WHEREAS,
the Lenders executing below have agreed to such amendment of the Credit Agreement on the terms and subject to the conditions contained in this Fourth Amendment.

NOW,
THEREFORE, in consideration of the premises and the mutual covenants herein contained, and for other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the parties hereto agree as follows:

I. AMENDMENTS

1.1 The definition of "Applicable Percentage" in Section 1.1 of the Credit Agreement is hereby amended
and restated in its entirety to read as follows:



1.2
The definition of "Fifty Million Credit Agreement" in Section 1.1 of the Credit Agreement is hereby amended and restated in its entirety to read as follows:



1.3
The definition of "Permitted Acquisition" in Section 1.1 of the Credit Agreement is hereby deleted.

1.4
The definition of "Permitted Investments" in Section 1.1 of the Credit Agreement is hereby amended and restated in its
entirety to read as follows:



---



1.5
The definition of "Pro Forma Basis" in Section 1.1 of the Credit Agreement is hereby deleted.

1.6
Section 3.3(b)(ii) of the Credit Agreement is hereby amended and restated in its entirety to read as follows:



************



1.7 Section 6.16 of the Credit Agreement is hereby amended by deleting the phrase "and after giving effect to any Permitted Acquisition" in the third
sentence of such Section.

1.8
Section 7.2 of the Credit Agreement is hereby amended and restated in its entirety to read as follows:

7.2 Financial Covenants.





2

---



1.9 A new Section 7.16 is hereby added to the Credit Agreement to read as follows:

7.16 Sale of Pharmaceutical Packaging Services Business.

On or before December 31, 2000, the Administrative Agent shall have received evidence that the Borrower has entered into a definitive agreement for the
sale of the pharmaceutical packaging services business of the Borrower and its Subsidiaries (which sale may be consummated through one or more mergers or stock or asset sales).

1.10
Section 8.5 of the Credit Agreement is hereby amended and restated in its entirety to read as follows:

8.5 Sale or Lease of Assets.

No Credit Party will, nor will it permit any of its Subsidiaries to, convey, sell, lease, transfer or otherwise dispose of, in one
transaction or a series of transactions, all or any part of its business or assets whether now owned or hereafter acquired, including, without limitation, inventory, receivables, equipment, real
property interests (whether owned or leasehold), and securities, other than (a) any inventory sold or otherwise disposed of in the ordinary course of business; (b) the sale, lease,
transfer or other disposal by a Credit Party (other than the Borrower) of any or all of its assets to the Borrower or to another Credit Party; (c) obsolete, slow-moving, idle or
worn-out assets (including inventory) no longer used or useful in its business; (d) the transfer of assets which constitute a Permitted Investment; (e) the lease of assets as
provided in the Lease; (f) any issuance of capital stock by the Borrower to an employee of a Credit Party in connection with the exercise by such employee of an employee stock option; or
(g) such other transfer of assets if (i) such transfer is for fair market value, (ii) at the time of such transfer no Default or Event of Default exists and is continuing,
(iii) as a result of such transfer no Material Adverse Effect would occur or be reasonably likely to occur, and (iv) the Net Cash Proceeds from such transfer are used to prepay Loans in
accordance with the terms of Section 3.3(b)(ii).

1.11 Section 8.8 of the Credit Agreement is hereby amended and restated in its entirety to read as follows:

8.8 Restricted Payments.

No Credit Party will, directly or indirectly, nor will it permit its Subsidiaries to, (a) declare or pay any dividends or make
any other distribution upon any shares of its capital stock of any class (each such dividend or distribution a "Dividend Restricted Payment") or (b) purchase, redeem or otherwise acquire or
retire or make any provisions for redemption, acquisition or retirement of any shares of its capital stock of any class or any warrants or options to purchase any such shares (each such repurchase,
redemption, acquisition or retirement a "Stock Repurchase Restricted Payment"); provided that (i) any Subsidiary of the Borrower may make Dividend Restricted Payments or Stock Repurchase
Restricted Payments to the Borrower or a Guarantor, (ii) Dividend Restricted Payments in the form of stock may be paid pursuant to the Rights Plan and the Benefits Plans and (iii) as
long as no Default or Event of Default exists and is continuing, Dividend Restricted Payments may be made with respect to (A) the Benefits Plans of the type referred to in subsection
(a) and (b) of the definition of "Benefits Plans", (B) the Benefits Plans of the type referred to in

3

---

subsection (c), (d), (e) and (f) of the definition of "Benefits Plans" in an aggregate amount not to exceed $50,000,000 during the term of this Credit Agreement and (C) the Rights
Plans in an aggregate amount not to exceed $2,000,000 during the term of this Credit Agreement.

1.12 A new Section 8.11 is hereby added to the Credit Agreement to read as follows:

8.11 Limitation on Restricted Actions.

No Credit Party will, directly or indirectly, nor will it permit its Subsidiaries to, create or otherwise cause or suffer to exist or
become effective any encumbrance or restriction on the ability of any such Person to (a) pay dividends or make any other distributions to any Credit Party on its capital stock or with respect
to any other interest or participation in, or measured by, its profits, (b) pay any Indebtedness or other obligation owed to any Credit Party, (c) make loans or advances to any Credit
Party, (d) sell, lease or transfer any of its properties or assets to any Credit Party, or (e) grant Liens on or security interests in its assets, except for such encumbrances or
restrictions existing under or by reason of (i) this Credit Agreement and the other Credit Documents, (ii) the Fifty Million Credit Agreement and the other Credit Documents (as defined
in the Fifty Million Credit Agreement), (iii) applicable law, (iv) any document or instrument governing Indebtedness incurred pursuant to Section 8.1(d),providedthat any
such restriction contained therein relates only to the fixed asset or assets purchased in connection therewith, (v) any
Permitted Lien or any document or instrument governing any Permitted Lien,providedthat any such restriction contained therein relates only to the
asset or assets subject to such Permitted Lien, (vi) customary restrictions and conditions contained in any agreement relating to the sale of any property permitted under Section 8.5
pending the consummation of such sale, (vii) the Amended and Restated Revolving Credit Agreement, dated as of August 29, 1997, between Covance Biotechnology Services Inc. and Bank
of America, N.A., formerly NationsBank, N.A or (viii) the Master Lease Agreement, dated as of May 27, 1999, between Chase Equipment Leasing, Inc., a New York corporation, and the
Borrower.

II. CONDITIONS PRECEDENT

2.1
This Fourth Amendment shall be effective upon the First Amendment to the Fifty Million Credit Agreement, dated as of the date hereof, becoming effective and upon receipt by the
Administrative Agent of each of the following:



4

---

III. MISCELLANEOUS

3.1 The term "Credit Agreement" as used in each of the Credit Documents shall hereafter mean the Credit Agreement as amended by this Fourth Amendment. Except
as herein specifically agreed, the Credit Agreement is hereby ratified and confirmed and shall remain in full force and effect according to its terms.

3.2
Each of the Credit Parties represents and warrants as follows:



3.3
This Fourth Amendment shall constitute a Credit Document.

3.4
The Guarantors acknowledge and consent to all of the terms and conditions of this Fourth Amendment and agree that this Fourth Amendment and all documents executed in connection
herewith do not operate to reduce or discharge the Guarantors' obligations under the Credit Documents.

3.5
In consideration of the Agents and the Required Lenders entering into this Fourth Amendment, the Credit Parties hereby release the Agents, such Lenders, and the Agents' and such
Lenders' respective officers, employees, representatives, agents, counsel and directors from any and all actions, causes of action, claims, demands, damages and liabilities of whatever kind or nature,
in law or in equity, now known or unknown, suspected or unsuspected to the extent that any of the foregoing arises from any action or failure to act on or prior to the date hereof.

3.6
This Fourth Amendment may be executed in any number of counterparts, each of which when so executed and delivered shall be an original, but all of which shall constitute one and
the same instrument.

3.7THIS FOURTH AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE
OF NEW YORK.

5

---

IN WITNESS WHEREOF, each of the parties hereto has caused a counterpart of this Fourth Amendment to be duly executed and delivered by their proper and duly authorized officer as of
the day and year first above written.

|BORROWER:   |  | COVANCE INC.,a Delaware corporation                                      
|----------- |  | -------------------------------------------------------------------------
|            |  | By:                                                                      
|            |  | Name:                                                                    
|            |  | Title:                                                                   
|GUARANTORS: |  | COVANCE PERIAPPROVAL SERVICES INC.,a Delaware corporation                
|            |  | By:                                                                      
|            |  | Name:                                                                    
|            |  | Title:                                                                   
|            |  | COVANCE PHARMACEUTICAL PACKAGING
SERVICES INC.,a Pennsylvania corporation
|            |  | By:                                                                      
|            |  | Name:                                                                    
|            |  | Title:                                                                   
|            |  | COVANCE LABORATORIES INC.,a Delaware corporation                         
|            |  | By:                                                                      
|            |  | Name:                                                                    
|            |  | Title:                                                                   
|            |  | COVANCE RESEARCH PRODUCTS INC.,a Pennsylvania corporation                
|            |  | By:                                                                      
|            |  | Name:                                                                    
|            |  | Title:                                                                   

6

---

| |  | COVANCE CENTRAL LABORATORY
SERVICES LIMITED PARTNERSHIP,an Indiana limited partnership  
| |  | ----------------------------------------------------------------------------------------
| |  | By Covance Central Laboratory Services Inc., a Delaware corporation, its General Partner
| |  | By:                                                                                     
| |  | Name:                                                                                   
| |  | Title:                                                                                  
| |  | COVANCE PRECLINICAL CORPORATION,a Washington corporation                                
| |  | By:                                                                                     
| |  | Name:                                                                                   
| |  | Title:                                                                                  
| |  | COVANCE CENTRAL LABORATORY SERVICES INC.,a Delaware corporation                         
| |  | By:                                                                                     
| |  | Name:                                                                                   
| |  | Title:                                                                                  
| |  | CJB INC.,a Delaware corporation                                                         
| |  | By:                                                                                     
| |  | Name:                                                                                   
| |  | Title:                                                                                  
| |  | COVANCE BIOTECHNOLOGY SERVICES INC.,a Delaware corporation                              
| |  | By:                                                                                     
| |  | Name:                                                                                   
| |  | Title:                                                                                  

7

---

|AGENTS:  |  | BANK OF AMERICA, N.A.,formerly NationsBank, N.A., in its capacity as
Administrative Agent and as a Lender
|-------- |  | ---------------------------------------------------------------------------------------------------------
|         |  | By:                                                                                                      
|         |  | Name:                                                                                                    
|         |  | Title:                                                                                                   
|LENDERS: |  | BANK OF MONTREAL                                                                                         
|         |  | By:                                                                                                      
|         |  | Name:                                                                                                    
|         |  | Title:                                                                                                   
|         |  | THE FUJI BANK, LIMITED                                                                                   
|         |  | By:                                                                                                      
|         |  | Name:                                                                                                    
|         |  | Title:                                                                                                   
|         |  | MORGAN GUARANTY TRUST COMPANY
OF NEW YORK                                                                
|         |  | By:                                                                                                      
|         |  | Name:                                                                                                    
|         |  | Title:                                                                                                   
|         |  | THE BANK OF NOVA SCOTIA                                                                                  
|         |  | By:                                                                                                      
|         |  | Name:                                                                                                    
|         |  | Title:                                                                                                   

8

---

| |  | BNP PARIBAS                   
| |  | ------------------------------
| |  | By:                           
| |  | Name:                         
| |  | Title:                        
| |  | By:                           
| |  | Name:                         
| |  | Title:                        
| |  | BARCLAYS BANK PLC             
| |  | By:                           
| |  | Name:                         
| |  | Title:                        
| |  | THE CHASE MANHATTAN BANK      
| |  | By:                           
| |  | Name:                         
| |  | Title:                        
| |  | CREDIT SUISSE FIRST BOSTON    
| |  | By:                           
| |  | Name:                         
| |  | Title:                        
| |  | By:                           
| |  | Name:                         
| |  | Title:                        
| |  | THE DAI-ICHI KANGYO BANK, LTD.
| |  | By:                           
| |  | Name:                         
| |  | Title:                        

9

---

| |  | BANK OF TOKYO  MITSUBISHI TRUST COMPANY
| |  | ----------------------------------------
| |  | By:                                     
| |  | Name:                                   
| |  | Title:                                  
| |  | MELLON BANK, N.A.                       
| |  | By:                                     
| |  | Name:                                   
| |  | Title:                                  
| |  | PNC BANK, NATIONAL ASSOCIATION          
| |  | By:                                     
| |  | Name:                                   
| |  | Title:                                  
| |  | THE SANWA BANK LTD.                     
| |  | By:                                     
| |  | Name:                                   
| |  | Title:                                  

10

---

QuickLinks