Rule 2.10 Announcement

Cambridge Antibody Tech Group PLC
25 May 2006

                                  ANNOUNCEMENT

FOR IMMEDIATE RELEASE

25 May 2006

                CAMBRIDGE ANTIBODY TECHNOLOGY GROUP PLC ("CAT")

                             RULE 2.10 ANNOUNCEMENT

CAT announces, in accordance with Rule 2.10 of the City Code on Takeovers and
Mergers, that subsequent to an issue of 4,640 ordinary shares under the CAT
Company Share Option Plan (OCSOP0), its issued share capital as at the 25
May 2006 comprises 53,200,125 ordinary shares of 10p each in issue (including
those represented by American Depositary Shares) ("CAT Shares").

The ISIN reference number for the CAT Shares is GB0001662252 and for the
American Depositary Shares of CAT is US1321481079.

Enquiries:

Justin Hoskins (Company Secretary), CAT

Tel: [phone]

END


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