Inclusion Criteria:

• Diagnosis of CLL as defined by the NCI-working group
• Previous treatment with standard systemic chemotherapy or immunotherapy.
• Disease progression or relapse after treatment.
• Indication for treatment as defined by the NCI Working Group Guidelines (Cheson, 1996)
• ECOG performance status ≤ 2
• Adequate liver and renal and bone marrow function

Exclusion Criteria:

• Treatment of CLL with chemotherapy, monoclonal antibody or radiotherapy within 60 days prior to entering the study. Acute toxicities from prior therapy must have resolved to Grade ≤ 1.
• Class 3 or 4 cardiac disease as defined by the New York Heart Association Functional Classification
• Severe or debilitating pulmonary disease (dyspnea at rest, significant shortness of breath, COPD)
• Active secondary malignancy or history of other malignancy within the last five years
• Active symptomatic fungal, bacterial and/or viral infection including active HIV or viral hepatitis (A, B or C).
• Patients who are contraindicated for treatment with rituximab
• Diagnosis of prolymphocytic leukemia, hairy cell leukemia, leukemic phase of non-Hodgkin's lymphoma, or other non-B-CLL B-cell malignancy;
• T-CLL or other T-cell malignancy