A myeloablative conditioning regimen incorporating daily intravenous busulfan, fludarabine, and 400 cGy total-body irradiation was given before allogeneic stem cell transplantation (SCT) to 64 adults with acute leukemia in first and second remission. Graft-versus-host disease (GVHD) prophylaxis included methotrexate, cyclosporine A, and rabbit antithymocyte globulin (Thymoglobulin). For 31 matched related (MRD) and 33 alternate donor (AD) SCT the incidence of acute GVHD grade II-IV was 11% +/- 6% versus 35% +/- 9% (P = .047), acute GVHD grade III-IV was 0% versus 10% +/- 6% (P = .09), and chronic GVHD was 40% +/- 9% versus 66% +/- 9% (P = NS), respectively. Overall transplant-related mortality (TRM) was 3% +/- 2%. Projected disease-free (DFS) and overall survival (OS) at 3 years for acute myelogenous leukemia (AML) (n = 36) are the same at 83% +/- 6%, and for acute lymphoblastic leukemia (ALL) (n = 28) are 65% +/- 10% and 78% +/- 8%, respectively. For MRD SCT DFS is 77% +/- 9%, OS 87% +/- 6%, for AD SCT the respective figures are 71% +/- 8% and 74% +/- 8%. OS and DFS in patients without and with high-risk features are 100% versus 71% +/- 7% (P = .007) and 88% +/- 8% versus 68% +/- 7% (P = .04), respectively. This combination appears relatively well tolerated, gives equivalent final outcomes from MRD and AD, and may be a reasonable alternative to conventional myeloablative regimens.