FIRST AMENDMENT

Exhibit 10.16(a)

FIRST AMENDMENT

     This First Amendment (this “Amendment”) is entered into as of December 11, 2006, by and among XXXXXX INTERNATIONAL INC., an Ohio corporation (“Borrower”), the Guarantors listed on the signature pages hereof, the Lenders signatory hereto, and UBS AG, STAMFORD BRANCH, as Administrative Agent for the Lenders (in such capacity, “Administrative Agent”).

RECITALS

     WHEREAS, Borrower, the Guarantors, the Lenders, the Administrative Agent, UBS SECURITIES LLC, as sole lead arranger and sole bookrunner, UBS AG, STAMFORD BRANCH, as issuing bank and collateral agent, UBS LOAN FINANCE LLC, as swingline lender, JPMORGAN CHASE BANK, N.A., as syndication agent, and KEYBANK NATIONAL ASSOCIATION, LASALLE BANK NATIONAL ASSOCIATION, and NATIONAL CITY BANK, as co-documentation agents, are parties to that certain Credit Agreement dated as of August 16, 2006 (the “Credit Agreement”) (capitalized terms used herein without definition have the meanings ascribed to such terms in the Credit Agreement);

     WHEREAS, Borrower has requested certain changes to Section 5.10 of the Credit Agreement;

     WHEREAS, the Administrative Agent and the Required Lenders have agreed to amend Section 5.10 of the Credit Agreement on the terms and subject to the conditions set forth herein;

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

          Section 1. Section References. Unless otherwise expressly stated herein, all Section references herein shall refer to Sections of the Credit Agreement.

          Section 2. Amendment of Section 5.10 (Interest Rate Protection). Section 5.10 is hereby amended by deleting the clause in its entirety and replacing it with the following:

No later than the 210th day after the Closing Date, Borrower shall enter into, and for a minimum of three years thereafter maintain, Hedging Agreements with terms and conditions reasonably acceptable to the Administrative Agent that result in at least 40% of the aggregate principal amount of Borrower’s Consolidated Indebtedness other than Revolving Loans being effectively subject to a fixed or maximum interest rate.

          Section 3. Conditions Precedent. The effectiveness of this Amendment is subject to the satisfaction of each of the following conditions precedent:

          (a) The Administrative Agent shall have received all of the following, in form and substance satisfactory to the Administrative Agent:

              (i) Amendment Documents. This Amendment, duly executed by the Borrower and the Guarantors (the “Amendment Documents”);

              (ii) Consent of Required Lenders. The written consent of the Required Lenders to this Amendment; and

              (iii) Additional Information. Such additional documents, instruments and information as the Administrative Agent may reasonably request to effect the transactions contemplated hereby.

          (b) The representations and warranties contained herein and in the Credit Agreement shall be true and correct in all material respects as of the date hereof as if made on the date hereof (except for those which by their terms specifically refer to an earlier date, in which case such representations and warranties shall be true and correct in all material respects as of such earlier date).

          (c) All corporate proceedings taken in connection with the transactions contemplated by this Amendment and all other agreements, documents and instruments executed or delivered pursuant hereto, and all legal matters incident thereto, shall be reasonably satisfactory to the Administrative Agent.

          (d) No Default or Event of Default shall have occurred and be continuing, after giving effect to this Amendment.

          Section 4. Representations and Warranties. The Borrower hereby represents and warrants to the Administrative Agent and the Lenders that, as of the date of and after giving effect to this Amendment, (a) the execution, delivery and performance of this Amendment and any and all other Amendment Documents executed and/or delivered in connection herewith have been authorized by all requisite corporate action on the part of the Borrower and will not violate the Borrower’s certificate of incorporation or bylaws, (b) all representations and warranties set forth in the Credit Agreement and in any other Loan Document are true and correct in all material respects as if made again on and as of such date (except those, if any, which by their terms specifically relate only to an earlier date, in which case such representations and warranties are true and correct in all material respects as of such earlier date), and (c) no Default or Event of Default has occurred and is continuing.

          Section 5. Survival of Representations and Warranties. All representations and warranties made in this Amendment or any other Loan Document shall survive the execution and delivery of this Amendment and the other Loan Documents, and no investigation by the Administrative Agent or the Lenders, or any closing, shall affect the representations and warranties or the right of the Administrative Agent and the Lenders to rely upon them.

          Section 6. Certain Waivers. Each of the Borrower and the Guarantors hereby agrees that neither the Administrative Agent nor any Lender shall be liable under a claim of, and hereby waives any claim against the Administrative Agent and the Lenders based on, lender liability (including, but not limited to, liability for breach of the implied covenant of good faith and fair dealing, fraud, negligence, conversion, misrepresentation, duress, control and interference, infliction of emotional distress and defamation and breach of fiduciary duties) as a result of the amendments contained in Section 2 above and any discussions or actions taken or not taken by the Administrative Agent or the Lenders on or before the date hereof or the discussions conducted in connection

therewith, or any course of action taken by the Administrative Agent or any Lender in response thereto or arising therefrom; provided, that the foregoing waiver shall not include the waiver of any claims which are based on the gross negligence or willful misconduct of the Administrative Agent or any Lender or any of their respective agents. This Section 6 shall survive the execution and delivery of this Amendment and the other Loan Documents and the termination of the Credit Agreement.

          Section 7. Reference to Agreement. Each of the Loan Documents, including the Credit Agreement, and any and all other agreements, documents or instruments now or hereafter executed and/or delivered pursuant to the terms hereof or pursuant to the terms of the Credit Agreement as amended hereby, are hereby amended so that any reference in such Loan Documents to the Credit Agreement, whether direct or indirect, shall mean a reference to the Credit Agreement as amended hereby.

          Section 8. Costs and Expenses. The Borrower shall pay on demand all reasonable out-of-pocket costs and expenses of the Administrative Agent (including the reasonable fees, costs and expenses of counsel to the Administrative Agent) incurred in connection with the preparation, execution and delivery of this Amendment.

          Section 9. Governing Law. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

          Section 10. Headings. Section Headings in this Amendment are included herein for convenience of reference only and shall not constitute a part of this Amendment for any other purposes.

          Section 11. Execution. This Amendment may be executed in any number of counterparts and by different parties hereto in separate counterparts, each of which when so executed shall be deemed to be an original and all of which taken together shall constitute one and the same agreement. Delivery of an executed counterpart of a signature page to this Amendment by telecopier shall be effective as delivery of a manually executed counterpart of this Amendment.

          Section 12. Limited Effect. This Amendment relates only to the specific matters covered herein, shall not be considered to be a waiver of any rights any Lender may have under the Credit Agreement (other than as expressly set forth herein), and shall not be considered to create a course of dealing or to otherwise obligate any Lender to execute similar amendments under the same or similar circumstances in the future.

          Section 13. Ratification By Guarantors. Each Guarantor hereby agrees to this Amendment, and each Guarantor acknowledges that such Guarantor’s Guarantee shall remain in full force and effect without modification thereto.

[signature pages follow]

     IN WITNESS WHEREOF, the parties hereto have caused this amendment to be executed by their respective officers thereunto duly authorized, as of the date first above written.

XXXXXX INTERNATIONAL INC.

By:

Name:

Title:

XXXXXX U.K. INC.

By:

Name:

Title:

ACER/EXCEL INC.

By:

Name:

Title:

AAC CONSULTING GROUP, INC.

By:

Name:

Title:

XXXXXX INTERNATIONAL CPU LLC

By:

Name:

Title:

XXXXXX AMERICAS HOLDING INC.

By:

Name:

Title:

XXXXXX AMERICAS INVESTMENT INC.

By:

Name:

Title:

XXXXXX AMERICAS MANAGEMENT INC.

By:

Name:

Title:

XXXXXX DELAWARE INC.

By:

Name:

Title:

XXXXXX NC INC.

By:

Name:

Title:

XXXXXX CLINICAL DEVELOPMENT SERVICES LIMITED (formerly known as Xxxxxxx River Laboratories Clinical Services International Ltd.)

By:

Name:

Title:

UBS AG, STAMFORD BRANCH,

as Administrative Agent

By:

Name:

Title:

By:

Name:

Title:

LENDERS:

By:

Name:

Title: