Dibromodulcitol and cyclophosphamide are both alkylating agents. In this study, these two drugs were compared for their effectiveness as remission maintenance therapy for childhood acute lymphoblastic leukemia or acute undifferentiated leukemia. Toxic effects were similar in both groups of patients although cystitis did not occur with the dibromodulcitol treatment. The duration of remission was slightly shorter for dibromodulcitol than for cyclophosphamide (P = 0.04). There was, however, a lower incidence of CNS leukemia in the patients treated with dibromodulcitol, which did not seem to be related to a basic difference in the patient groups.