THIS DEED OF VARIATION is made the 6 day of August 1998

BETWEEN

CIBA-GEIGY,  PLC (registered number 170180) whose registered office is at Hulley
Road, Macclesfield, Cheshire SK10 2NX ("the Vendor"); and

HUNTINGDON LIFE SCIENCES  LIMITED  (registered  number 1815730) whose registered
office is at Woolley Road, Alconbury, Huntingdon, Cambridgeshire, PE18 6ES ("the
Purchaser"); and

HUNTINGDON LIFE SCIENCES GROUP plc (formerly HUNTINGDON  INTERNATIONAL  HOLDINGS
PLC)  (registered  number  502370) whose  registered  office is at Woolley Road,
Alconbury, Huntingdon, (Cambridgeshire, PE18 6ES ("the Guarantor").

WHEREAS

A.       This Deed is  supplemental  to an Asset Purchase  Agreement  dated 14th
         March 1997 between the Vendor,  the Purchaser  and the  Guarantor  (the
         "Asset Purchase Agreement").

B. The Purchaser has requested amendment of the Asset Purchase Agreement.

C.       The  Vendor is  willing  to amend  the  timetable  for the  Purchaser's
         Payment obligations under the Asset Purchase Agreement.

D.       It is  desired  and  agreed  by the  parties  that the  Asset  Purchase
         Agreement be varied hereby.

NOW THIS DEED WITNESSETH as follows:

1.       In pursuance of the Asset Purchase  Agreement:  hereinbefore  mentioned
         and in  consideration  of the  provisions  hereinafter  contained IT IS
         HEREBY  AGREED AND DECLARED by and between the parties  hereto that the
         provision of the Asset  Purchase  Agreement be and hereby are varied in
         the manner following.

2.       Clause  4.3 of the Asset  Purchase  Agreement  shall be  deleted in its
         entirety and replaced with the following:

         "The Vendor acknowledges  receipt of the sum of  (pound)1,200,000  (the
         "Initial Consideration") paid by the Purchaser on completion.

         The balance of the Fixed  Consideration (the "Deferred  Consideration")
         shall  be  paid in cash on the  following  dates  and in the  following
         amounts:

         (a)    The sum of(pound)250,000 shall be paid on 14th September 1998;
         (b)    The sum of(pound)250,000 shall be paid on 14th December 1998;
         (c)    The sum of(pound)500,000 shall be paid on 14th  March 1999;
         (d)    The sum of(pound)500,000 shall be paid on 14th  June 1999;
         (e)    The sum of(pound)500,000 shall be paid on 14th September 1999;
         (f)    The sum of(pound)500,000 shall be paid on 14th December 1999;
         (g)    The sum of(pound)500,000 shall be paid on 14th  March 2000;
         (h)    The sum of(pound)500,000 shall be paid on 16th  June 2000;
         (i)    The sum of(pound)300,000 shall be paid on 14th September 2000."

3.       The Vendor hereby releases the Purchaser and the Guarantor from all and
         any  liabilities  and claims  (including  costs and interest) which may
         have  arisen  or may arise up to and  including  13th  September  1998,
         relating  to and/or  arising  out of Clause  4.3 of the Asset  Purchase
         Agreement  (or any breach or alleged  breach  thereof)  which clause is
         deleted in the entirety and replaced pursuant to Clause 2 of this Deed.

4.       This  Deed  shall be  governed  by and  construed  on all  respects in
         accordance  with English Law and the parties hereby submit irrevocably
         to the exclusive jurisdiction of the English Courts.

5.       This Deed may be  executed  in any number of  counterparts, and by the
         parties  hereto in separate  counterparts, each of which when executed
         shall  constitute  an  original,   but  all  of  which  shall together
         constitute  one  and  the  same  instrument.  This  Deed  shall not be
         effective until each party has executed at least one counterpart.

IT IS HEREBY  AGREED  AND  DECLARED  that the  Asset  Purchase  Agreement shall
continue in full force and effect save as  modified  by the  provisions of this
Deed.


EXECUTED AS A DEED
by CIBA-GEIGY PLC
Acting through two Directors or a
Director and the Secretary



EXECUTED  AS A DEED by  HUNTINGDON  LIFE  SCIENCES LIMITED  Acting  through two
Directors or a Director and the Secretary




EXECUTED AS A DEED by  HUNTINGDON  LIFE  SCIENCES GROUP plc Acting  through two
Directors or a Director and a Secretary