THIS THIRD SUPPLEMENTAL DEED is made this 7th day of August 1998

BETWEEN:-

1.       HUNTINGDON LIFE SCIENCES GROUP PLC, a Company incorporated under the
         laws of England and Wales with registered number 502370 of Woolley
         Road, Alconbury, Huntingdon, Cambridgeshire PE18 6ES ("the Chargor");
         and

2.       NATIONAL WESTMINSTER BANK PLC of 3rd Floor, Juno Court, 24 Prescott
         Street, London E1 8BB as agent and trustee for the Secured Parties
         (the "Agent" which expression shall include all successor agents
         appointed from time to time).

WHEREAS

(A)      By a Facilities Agreement of even date herewith made between the
         Chargor (1), Huntingdon Life Sciences Limited (2), Huntingdon Life
         Sciences Inc. (3), the Secured Parties (therein called the "Banks")
         (4) and the Agent (5) ("the Facilities Agreement"), the Banks agreed
         to make available to the Borrowers (as therein defined) certain
         facilities in substitution for the Existing Facilities (as therein
         defined);

(B)      The Existing Facilities, the Existing Ancillary Facilities and the
         Bridging Facility (as defined in the Facilities Agreement) are the
         only facilities which immediately prior to the signing of this Deed
         were available to the Borrowers from the Banks or any or them (alone
         or jointly with any other person);

(C)      This Deed is supplemental to a Guarantee and Debenture dated 1st
         November 1995 between the parties hereto (as amended and supplemented
         by Supplemental Deeds dated 20th January 1998 and 26th February 1998,
         together hereinafter referred to as "the Debenture")

NOW THIS DEED WITNESSETH as follows:-

1        (a)      In this Deed (including the recitals), unless the context
                  otherwise requires or unless otherwise defined or provided
                  for in this Deed, words and expressions shall have the same
                  meanings as are attributable to them under the Debenture and
                  the Facilities Agreement; and

         (b)      Clause 2.1 of the Debenture shall be amended by the
                  insertion of the words "when and to the extent that they fall
                  due for payment" after the words "that it will".

         2.       The right of the Agent to give notice and to take possession
                  and appoint a Receiver pursuant to Clause 7.1 of the Debenture
                  shall be exercisable only in accordance with Clause 13.4 of
                  the Facilities Agreement.

         3.       The provisions of Clause 7.2 of the Debenture shall, subject
                  to Clause 8 below, have effect only if, following a breach of
                  Clause 12.3(a) of the Facilities Agreement which constitutes
                  a Default under Clause 13.1(b) thereof or following a Default
                  described in Clause 13.1(f) thereof, the Agent gives notice
                  pursuant to Clause 13.2 of the Facilities Agreement and a
                  Receiver or Receivers are appointed over the whole of the
                  property, assets and undertaking of any of the Borrowers.

         4.       The Agent may only serve notice and exercise its rights under
                  Clause 10.1 of the Debenture if it has given notice in
                  accordance with Clause 13.2 of the Facilities Agreement.

         5.       The Agent may only serve notice and exercise its rights under
                  Clause 11.1 of the Debenture after notice has been given in
                  accordance with Clause 13.2 of the Facilities Agreement OR,
                  in the case of an application to the Court for an
                  administration order, only in the circumstances described in
                  Clause 13.1(j) of the Facilities Agreement.

         6.       Without prejudice to any set-off pursuant to insolvency
                  legislation and notwithstanding any other provisions of the
                  Debenture or this Deed, neither the Agent nor the  Secured
                  Parties (or any of them) shall have(i) any right  whether
                  under  Clause 14 of the  Debenture or otherwise
                  howsoever  to combine,  consolidate,  set off or  transfer
                  (save for a transfer  pursuant to Clause 14.2.3 of the
                  Facilities  Agreement)  any sums from time to time standing
                  to the credit of the Deposit Account or (ii) any rights or
                  remedies over such sums save for the exercise of the
                  Agent's rights under the Debenture in accordance with the
                  provisions of Clause 8 below.

         7.       The provisions of Clause 23 of the Debenture shall be subject
                  to any provisions inconsistent therewith in the Facilities
                  Agreement, which latter provisions shall prevail.

         8.       Notwithstanding any of the provisions of this Deed or the
                  Debenture:-

                  (a)  none of the rights, powers and remedies granted to the
                       Agent pursuant to the Debenture shall be exercisable in
                       relation to the sums from time to time standing to the
                       credit of the Deposit Account; and

                  (b)  the Chargor shall be entitled at all times to withdraw
                       monies from the Deposit Account for the general working
                       capital requirements of the Group, subject only to
                       Clause 14.2.2 of the Facilities Agreement;

                  unless (i) the Agent has made a demand for payment pursuant
                  to Clause 13.2 of the Facilities Agreement and has appointed
                  a Receiver or Receivers over the whole of the property,
                  assets and undertaking of any of the Borrowers pursuant to
                  Clause 11.1 of the Debenture as amended hereby OR (ii) an
                  administration order has been made in relation to any of the
                  Borrowers pursuant to section 8 of the Insolvency Act 1986
                  (or any statutory modification or re-enactment thereof from
                  time to time in force).

         9.       In the event of any inconsistency  between the provisions
                  hereof and the provisions of the Facilities Agreement the
                  latter shall prevail.

         10.      Subject to the provisions hereof the Debenture shall continue
                  in full force and effect.

         11.      This Deed shall be governed by and construed and interpreted
                  in accordance with English law.

         12.      Every provision contained in this Deed shall be severable and
                  distinct from every other such provision and if at any time
                  any one or more of such provisions is or becomes invalid,
                  illegal or unenforceable, the validity, legality and
                  enforceability of the remaining such provisions shall not in
                  any way be affected thereby.

         13.      This Deed may be executed in any number of counterparts and
                  all such counterparts shall be deemed to constitute one and
                  the same instrument.

IN WITNESS whereof the Chargor and the Agent have signed this Deed as a deed
with the intention that it be delivered the day and year first before written.


Signed as a Deed by                                  )
HUNTINGDON LIFE SCIENCES GROUP PLC                   )
acting by two Directors or one Director              )
and its Secretary                                    )


Signed as a Deed for and on behalf of                )
NATIONAL WESTMINSTER BANK PLC