Document:

<PAGE>

                                                                   Exhibit 10.5

       OUR REF  GECS/CAN.22.5/TMCA

       DATE     February 2001

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

Investment agreement

between

Inveresk Research Group Limited

Walter Nimmo and others

and

Candover Investments PLC and others

The rights attaching to the shares and loan stock to which this investment
agreement relates are subject to the terms of an inter-creditor agreement to be
entered into by, inter alia, the Company (as defined herein) and Bear Stearns
Corporate Lending Inc. as agent and security trustee.

--------------------------------------------------------------------------------
<PAGE>
<TABLE>
<CAPTION>
Contents                                                                    Page
--------                                                                    ----
<S>                                                                         <C>
1. Interpretation                                                              1
2. Conditions precedent                                                        4
3. Completion and subsequent matters                                           4
4. Fees and expenses                                                           5
5. Notices                                                                     6
6. Counterparts                                                                6
7. Applicable law                                                              6
</TABLE>

Schedules

Schedule 1  The Existing Manager
Schedule 2  The Investors
Schedule 3  Pre-Completion Shareholdings
Schedule 4  Post-Completion Shareholdings
Schedule 5  Conditions precedent

Agreed form of Documents

1.  Accountants' Report
2.  Articles
3.  CCRW Due Diligence Report
4.  Environmental Report
5.  Facility Agreement
6.  Insurance Report
7.  Merger Agreement
8.  New Loan Stock Instrument
9.  Market Report
10. Pensions Report
11. Stockholders Agreement
12. Resolutions (clause 1.2)
<PAGE>
THIS AGREEMENT IS MADE ON

between

(1)         INVERESK RESEARCH GROUP LIMITED (registered number 198206) having
            its registered office at Elphinstone Research Centre, Tranent,
            Edinburgh EH33 2NE (the "Company");

(2)         THE PERSONS whose names and addresses are set out in Schedule 1
            (together the "Existing Managers" and each an "Existing Manager");
            and

(3)         THE PERSONS whose names and addresses are set out in Schedule 2
            (together the "Investors" and each an "Investor")

WHEREAS

(A)         The Existing Managers and the Investors are the holders of the
            entire issued share capital of the Company, their current
            shareholdings being set out in Schedule 3.

(B)         The Further Investors have agreed to invest in the Company for the
            purposes of and subject to the terms and conditions of this
            Agreement.

(C)         The shareholdings in the Company following the investments
            contemplated by this Agreement are set out in Schedule 4.

IT IS HEREBY AGREED as follows:

1.          Interpretation

1.1         Unless the context otherwise requires, the following expressions
            used in this Agreement shall have the meanings set out below:

            "Accountants' Report" means the report prepared by Arthur Andersen
            relating to the Target Group and the documents annexed to such
            report all in the Agreed Terms;

            "Agreed Terms" means in the form, or substantially in the form,
            initialled for purposes of identification by or on behalf of the
            parties or, in the case of any document not so initialled, in the
            form executed by the parties thereto prior to or contemporaneously
            with Completion;

            "A Ordinary Shares" means cumulative convertible participating A
            ordinary shares of (pound)1 each in the capital of the Company
            having the rights, and being subject to the restrictions, set out in
            the Articles;

            "Articles" means the new articles of association of the Company in
            the Agreed Terms;

            "Bank" means Bear Stearns Corporate Lending Inc. as agent for and on
            behalf of the Finance Parties (as such term is defined in the
            Facility Agreement);

            "B Ordinary Shares" means convertible B ordinary shares of (pound)1
            each in the capital of the Company having the rights and being
            subject to the restrictions set out in the Articles;
<PAGE>
                                       2

            "Business Day" means a day (excluding Saturdays) on banks are
            generally open in London for the transaction of normal banking
            business;

            "CCRW" means Clifford Chance Rogers & Wells;

            "CCRW Due Diligence Report" means a report in Agreed Terms by CCRW
            addressed to, inter alia, the Company and the Investors' Agent
            concerning legal due diligence they have conducted in relation to
            the Target Group;

            "Closing" means satisfaction of the Minimum Condition (as such term
            is defined in the Merger Agreement) under the Tender Offer as
            provided for in the Merger Agreement;

            "Completion" means the occurrence of the events set out in Clause
            3.1;

            "Completion Date" means the date on which Closing occurs or such
            later date as may be agreed in writing by the parties hereto;

            "Environmental Report" means the report in the Agreed Terms prepared
            by Marsh UK Limited in relation to certain environmental matters
            affecting the Target Group addressed to, inter alia, the Company and
            the Investors' Agent;

            "Facility Agreement" means the facility agreement of even date with
            this Agreement between, inter alia, the Bank and the Company in the
            Agreed Terms;

            "Further Investors" means the Investors other than RBS Mezzanine
            Limited;

            "Insurance Report" means the report in the Agreed Terms prepared by
            Marsh UK Limited addressed to, inter alia, the Company and the
            Investors' Agent;

            "Investors' Agent" means Candover Partners Limited, 20 Old Bailey,
            London EC4M 7LN in its capacity as agent for the Further Investors;

            "Loan Stock Instrument" means the loan stock instrument dated 4
            September 1999 as amended by the New Loan Stock Instrument;

            "Market Report" means the report in the Agreed Terms prepared by
            Technomark Consulting Services in relation to the business of the
            Target Group;

            "Merger Agreement" means the agreement and plan of merger in the
            Agreed Terms made between Inveresk Research (Canada) Inc, Indigo
            Acquisition Corp. and the Target in the Agreed Terms in terms of
            which Indigo Acquisition Corp. shall launch a tender offer for all
            of the outstanding stock of the Target and if such tender offer is
            successful, in terms of which the merger of Indigo Acquisition Corp.
            and the Target shall be effected;

            "Merger Documents" means the Merger Agreement, the Stockholders
            Agreement and all other documents executed in connection with either
            of those documents;
<PAGE>
                                       3

            "New Loan Stock" means the (pound)44,734,481 loan stock of the
            Company constituted or to be constituted by the Loan Stock
            Instrument;

            "New Loan Stock Instrument" means the supplemental loan stock
            instrument supplementing and varying the loan stock instrument dated
            4 September 1999 in the Agreed Terms;

            "Ordinary Shares" means ordinary shares of (pound)1 each in the
            capital of the Company having the rights, and being subject to the
            restrictions, set out in the Articles;

            "Pensions Report" means the report in the Agreed Terms prepared by
            William M Mercer Inc and William M Mercer Limited addressed to,
            inter alia, the Company and the Investors' Agent;

            "Reports" means the Accountants' Report, the CCRW Due Diligence
            Report, the Environmental Report, the Insurance Report, the Market
            Report and the Pensions Report and "Report" means any of them;

            "Stockholders Agreement" means the stockholders agreement (as such
            term is defined in the Merger Agreement) in the Agreed Terms;

            "Subscription Shares" means the shares in the capital of the Company
            to be subscribed for by the Further Investors as provided by this
            Agreement;

            "Target Group" means the Target and its subsidiaries;

            "Target" means Clintrials Research Inc., a Delaware corporation;

            "Target Stock" means the Company Common Stock (as such term is
            defined in the Merger Agreement); and

            "Tender Offer" means the Offer (as such term is defined in the
            Merger Agreement).

1.2         Unless the context otherwise requires, where words and expressions
            used in this Agreement are defined in the Companies Act 1985 (the
            "Act") such words and expressions shall have the meanings attached
            to them respectively by the Act.

1.3         References in this Agreement to any statute or statutory provision
            shall be deemed to include references to any statute or statutory
            provision which amends, extends, consolidates or replaces the same
            (other than any such statute or statutory provision with
            retrospective effect to the extent that it is retrospective) and
            except to the extent that any amendments or modification enacted
            after the date of this Agreement would extend or increase the
            liability of any party to any other party under this Agreement and,
            save as aforesaid, to any order, regulation, instrument or other
            subordinate legislation made thereunder.

1.4         Reference to "Recitals", "Clauses" and "Schedules" and to
            sub-divisions thereof are to recitals and clauses of and the
            schedules to this Agreement and sub-divisions thereof. The Schedules
            shall form part of this Agreement.
<PAGE>
                                       4

1.5         The headings in this Agreement are for convenience only and shall
            not affect its construction or interpretation.

1.6         Unless the context otherwise requires:

1.6.1       words denoting the singular shall include the plural and vice versa;

1.6.2       words denoting a gender shall include all genders; and

1.6.3       references to persons shall include natural persons, bodies
            corporate, unincorporated associations, partnerships, joint
            ventures, trusts or other entities or organisations of any kind,
            including (without limitation) government entities (or political
            subdivisions or agencies or instrumentalities thereof).

2.          Conditions precedent

2.1         Completion is conditional upon the satisfaction or fulfilment (or
            waiver in writing or deemed waiver by the Investors' Agent) of the
            conditions set out in Schedule 5 on or prior to the Completion Date
            and the same continuing to be fulfilled or satisfied at Completion.

2.2         The Company shall use its reasonable endeavours to procure that the
            conditions precedent set out in Schedule 5 are satisfied on or
            before the Completion Date. The Company shall give notice promptly
            to the Further Investors upon all such conditions precedent having
            become satisfied or waived.

2.3         If the conditions set out in Schedule 5 are not satisfied on or
            before the Completion Date, the Investors' Agent shall be entitled
            forthwith by notice in writing to the Company to terminate this
            Agreement, whereupon none of the parties hereto shall be under any
            liability whatsoever to any other and the Further Investors shall
            not be bound to subscribe for any share of the Company pursuant to
            this Agreement or otherwise.

2.4         The Investors' Agent may waive in writing (at its sole and absolute
            discretion and whether on further terms and/or conditions or not as
            it thinks fit) any or all of the conditions set out in Schedule 5 if
            they have not been fully satisfied in accordance with Clause 2.1
            and, unless otherwise agreed, will be deemed to have so waived all
            of such conditions upon the Further Investors making payment of the
            subscription monies due on the Subscription Shares.

3.          Completion and subsequent matters

3.1         Completion shall take place at 3 Glenfinlas Street, Edinburgh or
            such other place as the parties shall agree on the Completion Date
            when the Further Investors shall each subscribe (or provide that
            their respective nominees subscribe) in cash for the number of A
            Ordinary Shares and nominal amount of New Loan Stock and for the
            consideration set out opposite their respective names in Schedule 2,
            each such subscription to be by way of telegraphic transfer to such
            account or in such manner as the Further Investors shall have been
            notified in writing by or on behalf of the Company prior to the
            Completion Date; and, subject to the Further Investors complying
            with these provisions, the Company shall allot and issue the A
            Ordinary Shares and New Loan Stock to the Further Investors (or
            their respective nominees) and shall enter the names of the
            allottees in the register of members (or Loan
<PAGE>
                                       5

            Stock holders as appropriate) of the Company and shall issue and
            deliver to the Further Investors share and Loan Stock certificates
            duly executed by the Company for the shares and New Loan Stock
            subscribed by them (or their respective nominees).

3.2         The proceeds of the subscription shall be used by the Company for
            the purpose of paying part of the consideration due under the Tender
            Offer and/or Merger Agreement and paying the costs and expenses in
            connection with the acquisition of the Target Stock.

3.3         As soon as practicable following Completion the Company shall
            procure that each of the Facility Agreement and the Merger Agreement
            is completed to the extent not already completed.

3.4         The Investors hereby consent to the grant as soon as practicable
            following Completion of the following exit based options over
            Ordinary Shares:-

3.4.1       to Walter Nimmo an option over 1,606 Ordinary Shares;

3.4.2       to Alastair McEwan an option over 2,460 Ordinary Shares;

3.4.3       to Nick Thornton an option over 5,460 Ordinary Shares; and

3.4.4       to Brian Bathgate an option over 1,282 Ordinary Shares;

            provided that each option shall be in a form approved by the
            Investors' Agent, acting reasonably.

3.5         Each of the parties hereby consents to the transactions contemplated
            by this Agreement (including, without limitation, the allotment and
            issue to the Further Investors of the Subscription Shares). Each of
            the parties shall execute all such other documents and do all such
            other acts and things, or procure the execution of such other
            documents or the performance of all such other acts and things, as
            shall be reasonably required in order to perfect the transactions
            intended to be effected under or pursuant to this Agreement.

4.          Undertakings

            The Company undertakes to the Investors that both before and after
            Completion:

4.1         there will be no amendment, modification or variation of the terms
            or conditions of the Merger Documents nor any waiver or consent
            granted thereunder without the prior written consent of the
            Investors' Agent;

4.2         the Merger Agreement shall not be terminated after the Tender Offer
            has closed; and

4.3         the Tender Offer will not be withdrawn after the Tender Offer has
            closed.
<PAGE>
                                       6

5.          Transfers of A Ordinary Shares

            Subject only to Completion taking place, RBS Mezzanine Limited
            agrees and undertakes that it will gift up to 10,375 A Ordinary
            Shares to one or more of the Further Investors as the Investors'
            Agent shall direct and further agrees and undertakes to execute and
            deliver to the Investors' Agent stock transfer forms to implement
            such transfers promptly on demand.

6.          Fees and expenses

            The Company shall pay the Investors' Agent an arrangement fee equal
            to (pound)420,000 (plus any VAT). Such fee shall be payable on the
            date of this Agreement. All legal and accountancy fees (plus any
            expenses and VAT) of the Further Investors in relation to this
            Agreement shall be for the account of the Company and shall be
            payable on the date of this Agreement or otherwise on demand.

7.          Notices

7.1         Any notices or other document to be served under this Agreement may
            be delivered or sent by facsimile to the party to be served at its
            address appearing in this Agreement or at such other address as it
            may have notified to the other parties in accordance with this
            Clause and shall (where the party to be served is not an individual)
            be marked for the attention of the individual specified in this
            Agreement or such other individual as the relevant party may have
            notified to the other parties in accordance with this Clause.

7.2         Any notice or document shall be deemed to have been served:

7.2.1       if delivered, at the time of delivery; or

7.2.2       if sent by facsimile, the time of despatch.

7.3         In proving service of a notice or document it shall be sufficient to
            prove that delivery was made or that the facsimile message was
            properly addressed and despatched as the case may be.

8.          Counterparts

            This Agreement may be executed in any number of counterparts and by
            the parties to it on separate counterparts, each of which shall be
            an original, but all of which together shall constitute one and the
            same instrument.

9.          Applicable law

            This Agreement shall be governed by and construed in accordance with
            English law and all the parties hereto irrevocably submit to the
            non-exclusive jurisdiction of the High Court in London as regards
            any claim, dispute or matter arising out of or relating to this
            Agreement or any of the documents to be executed pursuant to it.

AS WITNESS WHEREOF this Agreement has been executed on the date first above
written.
<PAGE>
                                       7

                                   Schedule 1

                             The Existing Managers

<TABLE>
<CAPTION>
              Name                                 Address
              ----                                 -------
<S>                            <C>
(1)   Walter Nimmo
(2)   Ian Sword
(3)   Stewart Leslie
(4)   Dr Brian Bathgate
(5)   Mr Alastair McEwan
(6)   Dr Norma Kellet
(7)   Ms Doreen Davidson
(8)   Mr Brian Cameron
(9)   Dr Malcolm Macnaughton
(10)  Dr Steve Freestone
(11)  Mr Alan Johnston
(12)  Dr Duncan Lawrence
(13)  Mr Rick Greenough
</TABLE>
<PAGE>
                                       8

                                   Schedule 2

                                 The Investors

<TABLE>
<CAPTION>
     (1)                                         (2)                  (3)                  (4)

Name & Address                             Number of New A   Nominal Value of New     Consideration
--------------                             Ordinary Shares        Loan Stock          -------------
                                           ---------------        ----------
                                                                    (pound)              (pound)
<S>                                        <C>               <C>                      <C>
Candover Investments PLC                        27,966             5,262,880             5,290,846
20 Old Bailey
London EC4M 7LN

Candover (Trustees) Limited                     3,107                Nil                   3,107
20 Old Bailey
London EC4M 7LN

Candover 1997 UK No 1 Limited                   90,984            15,409,712            15,500,696
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 UK No 2 Limited                   28,340             4,799,747             4,828,087
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 1 Limited                   75,541            12,794,062            12,869,603
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 2 Limited                   25,419             4,305,036             4,330,455
Partnership, 20 Old Bailey,  London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 3 Limited                   12,771             2,163,044             2,175,815
Partnership), 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

RBS Mezzanine Limited, 42 St                      Nil                 Nil                   Nil
Andrew Square, Edinburgh EH2 2YE

John Urquhart                                   1,391                 Nil                 15,000

Total                                          265,519            44,734,481            45,013,609
                                               =======            ==========            ==========
</TABLE>
<PAGE>
                                       9

                                   Schedule 3

                          Pre-Completion Shareholdings

<TABLE>
<CAPTION>
(1)                                                        (2)                                            (3)

Name & Address                                  Number and class of Shares                    Nominal value of loan stock
--------------                                  --------------------------                    ---------------------------
<S>                                             <C>                                           <C>
Dr Walter Nimmo                                   31,797 Ordinary Shares                                  Nil

Dr Norma Kellet                                    3,000 Ordinary Shares                                  Nil

Mr Stewart Leslie                                  8,672 Ordinary Shares                                  Nil

Dr Brian Bathgate                                  3,000 Ordinary Shares                                  Nil

Ms Doreen Davidson                                 3,000 Ordinary Shares                                  Nil

Mr Alastair McEwan                                 3,000 Ordinary Shares                                  Nil

Mr Brian Cameron                                   3,000 Ordinary Shares                                  Nil

Dr Malcolm Macnaughton                             3,000 Ordinary Shares                                  Nil

Dr Steve Freestone                                 3,000 Ordinary Shares                                  Nil

Mr Alan Johnston                                   3,000 Ordinary Shares                                  Nil

Dr Duncan Lawrence                                 3,000 Ordinary Shares                                  Nil

Dr Ian Sword                                      14,453 Ordinary Shares                                  Nil

Mr Rick Greenough                                  3,000 Ordinary Shares                                  Nil
</TABLE>
<PAGE>
                                       10

<TABLE>
<CAPTION>
(1)                                                        (2)                                            (3)

Name & Address                                  Number and class of Shares                    Nominal value of loan stock
--------------                                  --------------------------                    ---------------------------
<S>                                            <C>                                            <C>
Candover Investments PLC                        46,895 A Ordinary Shares                           (pound)3,065,201
20 Old Bailey
London EC4M 7LN

Candover (Trustees) Limited                     5,210 A Ordinary Shares                                  Nil
20 Old Bailey
London EC4M 7LN

Candover 1997 UK No 1 Limited                  152,564 A Ordinary Shares                           (pound)8,974,911
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 UK No 2 Limited                   47,521 A Ordinary Shares                           (pound)2,795,464
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 1 Limited                  126,667 A Ordinary Shares                           (pound)7,451,506
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 2 Limited                   42,622 A Ordinary Shares                           (pound)2,507,335
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 3 Limited                   21,415 A Ordinary Shares                           (pound)1,259,798
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

RBS Mezzanine Limited, 42 St                    16,715 A Ordinary Shares                           (pound)983,285
Andrew Square, Edinburgh EH2 2YE

John Urquhart                                    2,891 A Ordinary Shares                                  Nil

</TABLE>
<PAGE>
                                       11

                                   Schedule 4

                         Post-Completion Shareholdings

<TABLE>
<CAPTION>
(1)                                                     (2)                                (3)

Name & Address                               Number and class of Shares        Nominal value of loan stock
--------------                               --------------------------        ---------------------------
<S>                                          <C>                               <C>
Dr Walter Nimmo                                31,797 Ordinary Shares                      Nil

Dr Norma Kellet                                3,000 Ordinary Shares                       Nil

Mr Stewart Leslie                              8,672 Ordinary Shares                       Nil

Dr Brian Bathgate                              3,000 Ordinary Shares                       Nil

Ms Doreen Davidson                             3,000 Ordinary Shares                       Nil

Mr Alastair McEwan                             3,000 Ordinary Shares                       Nil

Mr Brian Cameron                               3,000 Ordinary Shares                       Nil

Dr Malcolm Macnaughton                         3,000 Ordinary Shares                       Nil

Dr Steve Freestone                             3,000 Ordinary Shares                       Nil

Mr Alan Johnston                               3,000 Ordinary Shares                       Nil

Dr Duncan Lawrence                             3,000 Ordinary Shares                       Nil

Dr Ian Sword                                   14,453 Ordinary Shares                      Nil

Mr Rick Greenough                              3,000 Ordinary Shares                       Nil

</TABLE>
<PAGE>
                                       12

<TABLE>
<CAPTION>
(1)                                                     (2)                                (3)

Name & Address                               Number and class of Shares        Nominal value of loan stock
--------------                               --------------------------        ---------------------------
<S>                                          <C>                               <C>
Candover Investments PLC                       74,861 A Ordinary Shares                8,328,081
20 Old Bailey
London EC4M 7LN

Candover (Trustees) Limited                    8,317 A Ordinary Shares                     Nil
20 Old Bailey
London EC4M 7LN

Candover 1997 UK No 1 Limited                  243,548 A Ordinary Shares            (pound)24,384,623
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 UK No 2 Limited                  75,861 A Ordinary Shares             (pound)7,595,211
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 1 Limited                  202,208 A Ordinary Shares            (pound)20,245,568
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 2 Limited                  68,041 A Ordinary Shares             (pound)6,812,371
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

Candover 1997 US No 3 Limited                  34,186 A Ordinary Shares             (pound)3,422,842
Partnership, 20 Old Bailey, London
EC4M 7LN acting by their general
partner Candover Partners Limited

RBS Mezzanine Limited, 42 St                   16,715 A Ordinary Shares              (pound)983,285
Andrew Square, Edinburgh EH2 2YE

John Urquhart                                  4,282 A Ordinary Shares                     Nil

</TABLE>
<PAGE>
                                       13

                                   Schedule 5

                              Conditions precedent

1.          The Investors' Agent having received all of the following:

1.1         a certified true copy of the Merger Documents (and of all
            agreements, indemnities, deeds and documents to be executed and/or
            delivered in terms thereof) all as duly executed; and

1.2         evidence that there have been duly passed resolutions of the Company
            in the Agreed Terms, inter alia, creating and authorising the
            allotment of the Subscription Shares, adopting the Articles as the
            articles of association of the Company and adopting the New Loan
            Stock Instrument.

2.          The Minimum Condition (as such term is defined in the Merger
            Agreement) having been satisfied in terms of the Merger Agreement.

3.          The Company having confirmed (acting reasonably, in good faith and
            after consultation with the Investors' Agent) to the Investors'
            Agent that all conditions set out in Annex A of the Merger Agreement
            have been satisfied or (with the consent of the Investors' Agent)
            waived.

4.          The Company having confirmed (acting reasonably, in good faith and
            after consultation with the Investors' Agent) to the Investors'
            Agent that no event has occurred which has had a material adverse
            effect on the financial condition of the Company and its
            subsidiaries taken as a whole.

5.          The Facility Agreement having become unconditional in all respects
            except insofar as it is conditional upon this Agreement having
            become unconditional and there having been no waiver, modification
            or variation of its terms or conditions nor any waiver or consent
            granted thereunder in any case without the prior written consent of
            the Investors' Agent.
<PAGE>
                                       14

Signed as a deed for and on behalf of           )
Inveresk Research Group Limited                 )  /s/ Walter Nimmo
                                                   __________________
by Walter Nimmo, Director                       )  Director
and Stewart Leslie, Director                    )

                                                   /s/ Stewart Leslie
                                                   __________________
                                                   Director

Signed as a deed by Walter Nimmo                )  /s/ Walter Nimmo
                                                   __________________
in the presence of this witness:                )  Walter Nimmo

Witness    /s/ Ewan Gilchrist

Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor

Signed as a deed by Ian Sword                   )  /s/ Walter Nimmo
                                                   __________________
by Walter Nimmo, his attorney                   )  Attorney
in the presence of this witness:                )

Witness    /s/ Ewan Gilchrist

Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor

Signed as a deed by Stewart Leslie              )  /s/ Stewart Leslie
                                                   __________________
in the presence of this witness:                )  Stewart Leslie

Witness    /s/ Ewan Gilchrist

Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor
<PAGE>
                                       15

Signed as a deed by Brian Bathgate              )  /s/ Walter Nimmo
by Walter Nimmo, his attorney                   )  ____________________________
in the presence of this witness:                )  Attorney

Witness    /s/ Ewan Gilchrist
           __________________________________

Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor

Signed as a deed by Alastair McEwan             )  /s/ Walter Nimmo
by Walter Nimmo, his attorney                   )  ____________________________
in the presence of this witness:                )  Attorney

Witness    /s/ Ewan Gilchrist
           __________________________________

Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor

Signed as a deed by Norma Kellet                )  /s/ Walter Nimmo
by Walter Nimmo, her attorney                   )  ____________________________
in the presence of this witness:                )  Attorney

Witness    /s/ Ewan Gilchrist
           __________________________________

Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor

Signed as a deed by Doreen Davidson             )  /s/ Walter Nimmo
by Walter Nimmo, her attorney                   )  ____________________________
in the presence of this witness:                )  Attorney

Witness    /s/ Ewan Gilchrist
           __________________________________

Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor
<PAGE>
                                       16

                                                   /s/ Walter Nimmo
Signed as a deed by Brian Cameron               )  -----------------------------
by Walter Nimmo, his attorney                   )  Attorney
in the presence of this witness:                )

Witness    /s/ Ewan Gilchrist
           ----------------------------------
Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor
                                                   /s/ Walter Nimmo
Signed as a deed by Malcolm Macnaughton         )  -----------------------------
by Walter Nimmo, his attorney                   )  Attorney
in the presence of this witness:                )

Witness    /s/ Ewan Gilchrist
           ----------------------------------
Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor
                                                   /s/ Walter Nimmo
Signed as a deed by Steve Freestone             )  -----------------------------
by Walter Nimmo, his attorney                   )  Attorney
in the presence of this witness:                )

Witness    /s/ Ewan Gilchrist
           ----------------------------------
Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor
                                                   /s/ Walter Nimmo
Signed as a deed by Alan Johnston               )  -----------------------------
by Walter Nimmo, his attorney                   )  Attorney
in the presence of this witness:                )

Witness    /s/ Ewan Gilchrist
           ----------------------------------
Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor
<PAGE>
                                       17

                                                   /s/ Walter Nimmo
Signed as a deed by Duncan Lawrence             )  -----------------------------
by Walter Nimmo, his attorney                   )  Attorney
in the presence of this witness:                )

Witness    /s/ Ewan Gilchrist
           ----------------------------------
Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor
                                                   /s/ Walter Nimmo
Signed as a deed by Rick Greenough              )  -----------------------------
by Walter Nimmo, his attorney                   )  Attorney
in the presence of this witness:                )

Witness    /s/ Ewan Gilchrist
           ----------------------------------
Full Name  Ewan Caldwell Gilchrist

Address    11 Walker Street

           Edinburgh

           Solicitor

Signed as a deed for and on behalf of           )  /s/ Ian Gray
Candover Investments PLC                        )  -----------------------------
acting by Ian James Gray as their attorney      )  Attorney
in the presence of this witness:                )

Witness    /s/ Graeme E.C. Sloan
           ----------------------------------
Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor
<PAGE>
                                       18

Signed as a deed for and on behalf of           )  /s/ Ian Gray
Candover (Trustees) Limited                     )  -----------------------------
acting by Ian James Gray as their attorney      )  Attorney
in the presence of this witness:                )

Witness    /s/ Graeme E. C. Sloan
           ----------------------------------
Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor

Signed as a deed for and on behalf of           )  /s/ Ian Gray
Candover 1997 UK No.1 Limited Partnership       )  -----------------------------
acting by Ian James Gray as their attorney      )  Attorney
in the presence of this witness:                )

Witness    /s/ Graeme E. C. Sloan
           ----------------------------------
Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor

Signed as a deed for and on behalf of           )  /s/ Ian Gray
Candover 1997 UK No 2 Limited Partnership       )  -----------------------------
acting by Ian James Gray as their attorney      )  Attorney
in the presence of this witness:                )

Witness    /s/ Graeme E. C. Sloan
           ----------------------------------
Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor
<PAGE>
                                       19

Signed as a deed for and on behalf of           )  /s/ Ian Gray
Candover 1997 US No 1 Limited Partnership       )  -----------------------------
acting by Ian James Gray as their attorney      )  Attorney
in the presence of this witness:                )

Witness    /s/ Graeme E. C. Sloan
           ----------------------------------
Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor

Signed as a deed for and on behalf of           )  /s/ Ian Gray
Candover 1997 US No 2 Limited Partnership       )  -----------------------------
acting by Ian James Gray as their attorney      )  Attorney
in the presence of this witness:                )

Witness    /s/ Graeme E. C. Sloan
           ----------------------------------
Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor

Signed as a deed for and on behalf of           )  /s/ Ian Gray
Candover 1997 US No 3 Limited Partnership       )  -----------------------------
acting by Ian James Gray as their attorney      )  Attorney
in the presence of this witness:                )

Witness    /s/ Graeme E. C. Sloan
           ----------------------------------
Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor
<PAGE>
                                       20

Signed as a deed for and on behalf of           )  /s/ Hazel McIntyre
RBS Mezzanine Limited                           )  _____________________________
acting by Hazel McIntyre as its attorney        )  Attorney
in the presence of this witness:                )

            /s/ Graeme E.C. Sloan
Witness    __________________________________

Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor

Signed as a deed for and on behalf of           )  /s/ Ian Gray
John Urquhart acting by Ian James Gray as his   )  _____________________________
attorney in the presence of this witness:       )  Attorney

            /s/ Graeme E.C. Sloan
Witness    __________________________________

Full Name  Graeme Eoghan Campbell Sloan

Address    3 Glenfinlas Street

           Edinburgh

           Solicitor<PAGE>
                                                                    Exhibit 10.6

                           EDINBURGH

                           OUR REF   PEC/GECS/CAN.22.5

                           DATE       3 April 2001

                           Inveresk Research Group Limited

                           Instrument

                           Constituting L44,734,481 Unsecured
                           Subordinated Loan Stock 2008

                           This Instrument (together with the Original
                           Instrument (as defined herein)) is subject to the
                           terms of an Intercreditor Deed executed of even date
                           amongst, inter alia, the Company (as defined herein)
                           and Bear Stearns Corporate Lending Inc. as agent and
                           security trustee.

                           Maclay Murray [LOGO] Spens
                                   SOLICITORS

                           3 GLENFINLAS STREET
                           EDINBURGH EH3 6AQ

                           DX EDINBURGH BOX NO 137  TEL.:  0131 226 5196
<PAGE>
THIS INSTRUMENT is made by way of deed on 3rd April, 2001'

BY INVERESK RESEARCH GROUP LIMITED (registered number 198206) whose registered
office is at Elphinstone Research Centre, Tranent, Edinburgh EH33 2NE (the
"Company").

WHEREAS:

(A)      The Company, pursuant to a resolution of its board of directors passed
         on 20 September, 1999 created and authorised the issue of a maximum
         nominal amount of L27,037,500 Unsecured Subordinated Loan Stock 2008
         (the "Original Loan Stock") which loan stock was constituted pursuant
         to a loan note instrument dated 20 September, 1999 (the "Original
         Instrument").

(B)      In terms of Clause 10 of the Original Instrument, the Company may
         resolve to create and issue further loan stock identical in all
         respects and to form a single series with the Original Loan Stock.

(C)      The Company has, by resolution of its board of directors passed on 3
         April, 2001, created and authorised the further issue of a maximum
         nominal amount of L44,734,481 Unsecured Subordinated Loan Stock 2008
         (the "New Loan Stock") to be constituted on the same terms and
         conditions as the Original Instrument other than as amended by this
         Supplemental Instrument.

BY THIS DEED THE COMPANY DECLARES AND COVENANTS AS FOLLOWS:-

1.       Definitions and Interpretation

1.1      The definitions and rules of interpretation in Clause 1 of the Original
         Instrument shall apply to and govern the interpretation of this
         Supplemental Instrument as if references in the Original Instrument to
         "Loan Stock" included the New Loan Stock constituted by this
         Supplemental Instrument, unless the contrary is expressly stated and,
         in addition, the following words and expressions shall have the
         following meanings:

         "Bank" means Bear Stearns Corporate Lending Inc. as Agent for and on
         behalf of the Finance Parties (as such terms are defined in the
         Facilities Agreement between the Company and Bear Stearns Corporate
         Lending Inc. in various capacities dated 22 February, 2001) and its
         successors and assignees as Agent;

         "Intercreditor Deed" means the intercreditor deed dated on or around
         the date of this Instrument between, inter alia, Bear Stearns Corporate
         Lending Inc. and the Company.

1.2      With effect from the date of this Instrument the definition of "Bank"
         in the Original Instrument shall be deleted and replaced with the
         definition of "Bank" in this Supplementary Instrument.

1.3      With effect from the date of this Instrument the definition of
         "intercreditor agreement" in the Original Instrument shall be amended
         to read "means the intercreditor deed dated on or around 3 April, 2001
         between the Company, the Bank, the Stockholders and others as the same
         may be amended, or supplemented from time to time".

2.       Amount of the New Loan Stock

2.1      The aggregate nominal amount of the New Loan Stock constituted by this
         instrument is limited to L44,734,481.
<PAGE>
3.       Status of the Loan Stock

3.1      The New Loan Stock represents a direct and unsecured obligation of the
         Company for the due and punctual payment of the principal in respect of
         it and for the performance of all the obligations of the Company with
         respect to it.

3.2      Subject to the Intercreditor Deed, the New Loan Stock when issued will
         rank pari passu equally and rateably without discrimination or
         preference as unsecured obligations of the Company and with all other
         unsecured indebtedness of the Company expect to the extent provided by
         law.

3.3      The New Loan Stock shall form a single series with the Original Loan
         Stock.

4.       Interest

4.1      In Clause 7.1 of Schedule 2 to the Original Instrument, in relation to
         the New Loan Stock only, the references to 31 December, 1999 shall be
         deleted where they appear on the seventh and eighth lines thereof, and
         shall be substituted with 30 June, 2001.

4.2      In Clause 7.3 of the Original Instrument, the word "Loan" shall be
         added before the word "Stock" where it appears on the fourth and fifth
         lines thereof.

4.3      A new clause 7.7 shall be inserted at Schedule 2 to the Original
         Instrument, as follows:

              "7.7 Without prejudice to the Company's obligations hereunder,
                   where the Company fails to pay the interest due on any
                   Interest Payment Date on or after 31 December, 2001 (as a
                   result of any prohibition set out in the Inter Creditor Deed
                   or otherwise) that interest shall be added to the principal
                   amount of the Loan Stock on such Interest Payment Date (and
                   there shall also be added to the principal amount of the Loan
                   Stock on 30 June, 2001 all other interest which has become
                   due on any Interest Payment Date prior to that date but has
                   not been paid) and, for the avoidance of doubt, such interest
                   shall be treated as principal and thereafter interest thereon
                   shall accrue and shall be payable in accordance with the
                   provisions of this Instrument so that the term "Loan Stock"
                   when used in this Instrument shall include such unpaid
                   interest as if it has been principal from the date of this
                   Instrument."

4.4      Clause 7.7 of Schedule 2 to the Original Instrument shall be
         re-numbered Clause 7.8.

IN WITNESS whereof this instrument has been executed as a deed and has been
delivered on the date first above written.

EXECUTED as a deed by             )
INVERESK RESEARCH GROUP LIMITED   )
acting by:-                       )
                                  )
                                  )
Director /s/ Ian P. Sword         )
                                  )
Director/Secretary                )

         /s/ Walter Nimmo

                                       2

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00037-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00037-of-00352.parquet"}]]