OBJECTIVES: I. Determine the graft failure rate and overall survival of patients with severe aplastic anemia after receiving an allogeneic bone marrow transplant. II. Determine the efficacy of high dose cyclophosphamide and antithymocyte globulin as conditioning regimen for a second bone marrow transplant in patients who reject their first graft. III. Determine the efficacy of methylprednisolone and anti-CD3 monoclonal antibody as a conditioning regimen for a second bone marrow transplant in patients who reject their first graft and are poor candidates for cyclophosphamide and antithymocyte globulin.