A new combination of total lymphoid irradiation and cyclophosphamide was used prior to bone marrow transplantation in an attempt to achieve decreased rejection rates and graft-versus-host disease. Nine previously transfused patients with severe aplastic anemia received marrow from an HLA-identical, MLC-compatible sibling following this preparative regimen. There were no episodes of graft rejection, and only one patient developed graft-versus-host disease. Of the 9 patients, 7 (78%) are surviving with a median follow-up of 400 days. The excellent results of this pretransplant combination of total lymphoid irradiation and cyclophosphamide warrants application of this regimen to a larger series of patients.