From April 1976 through August 1989, 66 patients with aplastic anemia were treated on either of two immunosuppressive regimens in preparation for allogeneic bone marrow transplantation (BMT) from matched donor. Seventeen patients were treated with cyclophosphamide (50 mg/kg for 3 days) followed by thoracoabdominal irradiation (TAI), 6 Gy/1 fr and 2 patients, receiving marrow graft from partially matched family donors, were treated with cyclophosphamide (50 mg/kg for 3 days), TAI (6 Gy/1 fr) and Ara-C (4 g/mq for 2 days). Forty-seven more patients were treated with cyclophosphamide alone (50 mg/kg for 4 days). All patients received prophylactic treatment with methotrexate (15) or cyclosporine A (51) to avoid graft-versus-host disease. Mean time to engraftment was 12 days after chemotherapy and TAI and 15 days after cyclophosphamide (Cy) alone. No marrow rejections were observed in the TAI group: the two infants that received partially matched marrow allografted and are alive and well. Two patients treated with cyclophosphamide alone rejected allogeneic marrow. Long-term overall survivals are similar: 64% for TAI + Cy group and 56% for Cy alone group. In spite of the immunosuppressive regimen employed, young patients (under 20 years) do better than older ones (survival: 65% vs 45%, respectively). Thus, patient's age seems to be the main factor determining overall survival after allogeneic BMT. We conclude that the use of irradiation does not add significantly to the survival of aplastic patients; given the possible toxic long-term effects of irradiation, it would probably be wise to restrict the combined use of cyclophosphamide and irradiation to the patients sensitized to their donors, to those receiving partially matched marrow from family donors or in programs involving T-cell depletion.