Much progress has been made over the past year in our understanding of the cytogenesis, biology, and therapy of chronic lymphocytic leukemia (CLL). Further definition of common cytogenetic abnormalities in CLL make it appear that the identification of a new tumor suppressor gene is close at hand. Recent studies have also defined relationships between genetic abnormalities and leukemia cell phenotype and drug resistance that may assist in assessing prognosis or assigning therapy. We have achieved a better understanding of the surface antigens that help govern the pattern of tissue infiltration of leukemia cells in vivo. Studies of the immune pathophysiology of CLL are providing clues to potential mechanisms leading to the autoimmunity and immunodeficiency associated with this disease. The efficacy of purine analogues in CLL has been verified in multicenter clinical trials. Finally, new therapies incorporating bone marrow transplantation, and possibly gene therapy, are being considered more frequently for the therapy of patients with this disease.