Inclusion Criteria:

• At least 18 years old
• Written informed consent
• Confirmed diagnosis of CLL or SLL (small mature lymphocytes n blood, bone marrow or lymph nose expressing CD19, CD5, CD23, weakk CD79b, and weak clonally restricted immunoglobin light chain)
• p53 deletion by FISH in at least 20% of leukamia cells
• Treatment is indicated (Binet stage B or C, or stage A with a lyphocyte doubling time of less than 6 months, or disease-related symptoms or complications irrespective of clinical stage)
• WHO performance status 0, 1 or 2
• Both untreated and previously treated patients are eligible for study

Exclusion Criteria:

• Patients must have none of the following:

Active infection Known HIV infection Past history of anaphylaxis following exposure to rat or mouse CDR-grafted humanised monoclonal antibodies Less than 3 weeks since prior chemotherapy Use of prior investigational agents within 6 weeks Pregnancy or lactation Uncontrolled diabetes mellitus Uncontrolled hypertension Active peptic ulcer disease Other severe concurrent diseases or mental disorders Serum urea or creatinine more than twice the upper limit of normal (unless due to uretic obstruction or renal infiltration by CLL/SLL) Serum bilirubin more than twice the upper limit of normal (unless due to haemlysis or liver infiltration with CLL/SLL) Persisting severe cytopenias due to previous therapy rather than disease (neutrophils <0.5 x 109/l or platelets <50 x 10/l)