Inclusion Criteria:

• Patients with chronic lymphocytic leukemia (CLL), CLL/PLL (as defined by FAB [French-American-British Classification]), small lymphocytic lymphoma (SLL) and prolymphocytic leukemia (PLL) who have relapsed from or are refractory to at least one fludarabine-based regimen and no greater than 2 regimens.
• Absolute neutrophil count (ANC) >= 1 x 109/L and platelet count >= 50 x 109/L.
• Adequate organ function as indicated by the following laboratory values: serum creatinine </= 1 mg/dL; if serum creatinine > 1 mg/dL, then the estimated glomerular filtration rate (GFR) must be > 60 ml/min/1.73 m2 as calculated by the Modification of Diet in Renal Disease equation; serum bilirubin </= 1.5 mg/dL x ULN; aspartate transaminase (AST)or alanine transaminase (ALT) </= 2.5 x ULN; alkaline phosphatase </= 2.5 x ULN.
• ECOG performance status <= 2.
• Age >/= 18 years.

Exclusion Criteria:

• Patients with NYHA >/= grade 3 heart disease as assessed by history and/or physical examination.
• Pregnant or breastfeeding women or patients who are unwilling or unable to practice adequate contraception. Positive pregnancy test for women of child bearing potential (defined as not post-menopausal for 12 months or no previous surgical sterilization).
• Chemotherapy within 4 weeks of starting therapy, or concurrent anticancer therapy (chemotherapy, radiotherapy, or biologic therapy).
• Other malignancy within 3 years except in situ carcinoma.
• Unwilling or unable to provide informed consent.
• Known hypersensitivity to nucleoside analogues.
• Any other significant medical condition that compromises safety, compliance or study conduct, including but not limited to uncontrolled hypertension, unstable angina, myocardial infarction within 6 months, ventricular arrhythmia, active infection, and known hepatitis.