A previous phase I dose escalation study determined that the maximum tolerated doses of busulfan and cyclophosphamide that could be combined with 12.0 Gy of total body irradiation were 7 mg/kg and 50 mg/kg, respectively. A phase II study of these three agents was carried out in 56 patients with advanced myeloid malignancies receiving allogeneic bone marrow transplants from HLA-identical donors. Cyclosporine with methotrexate or with prednisone was administered for prophylaxis against graft-versus-host disease. Grade 3 (n = 8) and 4 (n = 3) regimen-related toxicity occurred in 20% of patients, which was the maximum predicted from the phase I study. The 2-year actuarial probabilities of non-relapse mortality and relapse were 0.52 and 0.55, respectively. Fourteen patients survive, 12 in remission, 581-1761 days post-transplant. The actuarial probabilities of disease-free survival for patients with recurrent acute myeloid leukemia and advanced chronic myeloid leukemia at 2 years were 20% and 23%, respectively. When compared with our historical experience in patients receiving other treatment regimens, there was no apparent improvement in disease-free survival.