This is a prospective study designed to determine the toxicity, efficacy and antileukemic effect of high-dose cytosine arabinoside (ara-C), cyclophosphamide and total body irradiation (TBI) as a myeloablative regimen prior to allogeneic bone marrow transplantation for patients with hematologic malignancies. Fifty-eight patients with hematologic malignancies were treated with cyclophosphamide, high-dose ara-C and total body irradiation (TBI) followed by allogeneic bone marrow transplantation. Fifty patients had good prognosis disease and eight had poor prognosis disease. Cyclosporine and short-course methotrexate were used for graft-versus-host disease (GVHD) prophylaxis. The conditioning regimen consisted of ara-C 3000 mg/m2 twice a day x six doses on days -7, -6, and -5; cyclophosphamide 1800 mg/m2 on days -4 and -3; and TBI 1400 cGy midline dose at 5 cGy/min in eight total fractions administered twice a day on days -4, -3, -2, and -1. The bone marrow was infused on day 0 (zero). Toxicity related to the conditioning regimen was comparable to that reported with other conditioning regimens, except for diarrhea which appears to be more frequent. The actuarial survival at 1 year was 69% (58-82) and at 5 years was 54% (42-69) with the numbers in parentheses representing the 95% confidence interval of the Kaplan-Meier estimate. After a median follow-up of 28 months, 31 of 58 (53%) patients are alive without evidence of disease. Only four of the 58 patients (7%) have relapsed. Cyclophosphamide, ara-C and TBI is a safe and effective myeloablative regimen for patients with leukemia. The overall relapse rate in our study was 7% with a median follow-up of 28 months and appears to be lower than relapse rates reported in other series. This is probably due to the added antileukemic effect of ara-C. This regimen should be compared with other myeloablative regimens in a controlled study.