Fifty-eight patients received an allogeneic or syngeneic marrow transplant following conditioning with high doses of dimethylbusulfan (DMB), cyclophosphamide (CY) and total body irradiation (TBI). Thirty-two patients had either chronic myeloid leukemia (CML) in accelerated phase or blast transformation, or acute leukemia after first relapse. The actuarial survival of these 32 patients at 3 years was 12% compared with 25% for a group of 206 patients with similar diagnoses prepared for transplantation with CY and TBI alone. This reduced survival was associated with a greater incidence of early non-leukemic deaths, in particular as a result of severe hepatic veno-occlusive disease. The incidence of leukemic relapse was not different in the two groups. Of 13 patients with CML in chronic phase who received syngeneic transplants following DMB, CY and TBI, nine are alive in hematologic and cytogenetic remission from 3.9 to 9.4 (median 6.2) years post-transplant.