EXHIBIT 26


                  [LETTERHEAD OF CAMBRIDGE ANTIBODY TECHNOLOGY]

Denis Mulhall
Fitzgeorge House
Fitzgeorge Avenue
New Maiden
Surrey KT3 4SH

                                                                 22 January 2003

Dear Mr Mulhall

Service Agreement with Oxford Glycosciences plc

We are writing to you in relation to the proposed merger of Oxford Glycosciences
plc with Cambridge Antibody Technology Group plc ("the Merger"), which is
proposed to be effected by a scheme of arrangement pursuant to section 425 of
the Companies Act 1985.

Subject to and conditionally upon the Merger becoming effective by 30 April
2003:

(a)   we would propose that Clause 20.1 of your service agreement with Oxford
      Glycosciences plc dated 25 September 2002 ("the Service Agreement") be
      varied to provide that you shall be entitled to give notice of your
      intention to terminate your employment at any time during the period of 12
      months following the date upon which the Merger becomes effective and
      that such right shall not be conditional upon there having been any
      material and detrimental change, as described in Clause 20.1 of your
      Service Agreement;

(b)   in consideration of this, you agree (without prejudice to your continuing
      employment with Oxford Glycosciences plc) at our request made at any time
      to resign promptly from the board of Oxford Glycosciences plc and from the
      board of any member of the Oxford Glycosciences group of companies without
      any claim against Oxford Glycosciences plc or any of the members of the
      Oxford Glycosciences group of companies, whether in relation to your
      employment with or office as a director of such companies, arising from
      such resignations. Should you fail to do so, the board of Cambridge
      Antibody Technology Group plc shall be irrevocably authorised to appoint
      some person in your name and on your behalf to sign any documents and take
      such other steps as are necessary to give effect to such resignations.

For the avoidance of doubt, the above variation would apply only to the Merger
and not to any other change of control that may take place after the Merger has
been implemented.

We should be grateful if you would confirm your agreement to the proposed
variation by executing this letter below. This letter may be executed in
counterparts and by the parties to it on separate counterparts, each of which
when so executed and delivered shall be an original, but both counterparts shal1
together constitute one and the same instrument.



EXECUTION:

Dated 22 January 2003

SIGNED AND DELIVERED as a DEED by               )
JOHN ASTON, Director and DIANE MELLETT,         )  /s/ [Illegible]
Secretary duly authorised for and on behalf of  )  /s/ [Illegible]
CAMBRIDGE ANTIBODY TECHNOLOGY GROUP PLC         )


SIGNED AND DELIVERED as a DEED by DENIS MULHALL )  /s/ [Illegible]
in the presence of                              )


Witness' signature                      /s/ C. Moyses
                                        ---------------------------------

Witness' name (in capitals)             C. MOYSES

Witness' Address                        THE OLD BARN, GREAT MILTON

Occupation:                             MEDICAL DIRECTOR