Between February 1985 and May 1988, sixteen patients with severe aplastic anemia (SAA) post multitransfusion were treated with either allogeneic bone marrow transplantation (BMT) (9) or immunosuppression (7). The latter group was further divided into two subgroups: horse anti-human thymocyte-lymphocyte globulin (ATG-ALG) (2) and high dose methylprednisolone (HDMP) (5). There were 8 males and 8 females, age ranged from 10 to 35 years for the BMT group and 19 to 56 for the immunosuppression group. As of analysis, 9 patients in the BMT group had been followed from 1 to 31 months after transplant (median,24). Graft rejection was noted in 2, both had positive mixed lymphocyte culture (MLC) index. Seven had full recovery of hematopoiesis. Of these 7 survivals, none developed acute graft-versus-host disease (GVHD), whereas 2 had chronic GVHD which resolved completely after a 9-month treatment with azathioprine and prednisolone. Kaplan-Meier survival probability at 31 month was 75%. In the immunosuppressive therapy group 2, who received ATG-ALG both failed the treatment, died 7 and 29 months later, respectively. There were 3 responders in the HDMP subgroup, 1 complete, 2 partial. The 1-year survival probability for this group was 42.9% compared with 75% in the BMT group (p greater than 0.10). However, the hematologic reconstitution and Karnofsky performance were complete in all 7 transplant survivals vs one of 3 in the immunosuppression group (p less than 0.01). This experience supports that for patients with SAA under the age of 40, BMT is the treatment of choice if an HLA-identical MLC-nonreactive marrow donor is available, if not, immunosuppression is an alternative approach.(ABSTRACT TRUNCATED AT 250 WORDS)