OUTLINE: All patients receive myeloablative therapy with high-dose cyclophosphamide and total body irradiation over 4 days; patients with severe aplastic anemia also receive antithymocyte globulin. Patients then undergo allogeneic bone marrow transplantation. Filgrastim (G-CSF) is given after transplant to accelerate engraftment. Sargramostim (GM-CSF) may be given in case of graft failure.