 Rationale: Research indicates that both cyclophosphamide and pentostatin work synergistically against cancer cells and have a high response rate against chronic lymphocytic leukemia CLL without creating severe side effects in patients. In addition, studies have shown that rituximab, a therapy that targets the immune system, has the highest efficacy against CLL and the lowest toxicity rate when compared with other immunotherapy drugs. Studies also show that rituximab enhances the efficacy of the chemotherapy agents cyclophosphamide and pentostatin. This study offers the combination of immunotherapy with two promising chemotherapy agents against CLL. 