 - Group I malignant disease or severe aplastic anemia severe aplastic anemia closed to accrual: Patients undergo total body irradiation TBI once or twice daily on days -8 to -4. Patients then receive cyclophosphamide IV on days -3 and -2, methylprednisolone IV on days -3 to 0, and antithymocyte globulin ATG IV once or twice daily on days -3 to -1. 