Thirty-four patients with chronic myelogenous leukemia in chronic phase were treated with busulfan 16 mg/kg and cyclophosphamide 120 or 200 mg/kg before allogeneic bone marrow transplantation from an HLA-identical sibling. Cyclosporine, methotrexate and prednisone were used for graft-versus-host disease (GVHD) prophylaxis. The actuarial probabilities of survival and relapse-free survival at 82 months were 71%. With a maximum follow-up of 2471 days, none of the patient experienced hematologic or clinical relapse. In one patient reappearance of host cells was documented 180 days post-transplant which disappeared 277 days post-transplant and the patient is in complete hematological and cytogenetic remission 5 years after the transplant. The probability of transplant-related mortality was 29% while the probability of moderate to severe acute graft-versus-host disease was 38%. This study indicates that busulfan and cyclophosphamide are a good conditioning regimen for marrow transplantation in patients with chronic myeloid leukemia in chronic phase.