The clinical use of chlorambucil in the treatment of chronic lymphocytic leukemia and malignant lymphomas was first reported in 1955 by Galton et al.1 Since that time many reports2-9 have confirmed the efficacy of this drug in the treatment of chronic lymphocytic leukemia. Because of its ease of administration and relative safety, chlorambucil is considered by many to be the therapeutic agent of choice. In 1958, another orally effective alkylating agent, cyclophosphamide (Cytoxan), was found to be effective against chronic lymphocytic leukemia.10-12 Further studies in this country showed cyclophosphamide to have a therapeutic efficacy approximating that of chlorambucil in the treatment of chronic lymphocytic leukemia.13-15 Since a direct and concurrent comparison between the two drugs had not been made, the Veterans Administration Cancer Chemotherapy Study Group decided to undertake such a study in 1960. Material and Methods All patients with an established diagnosis of chronic lymphocytic