In severe aplastic anemia, disease-dependent mortality was high before allogeneic bone marrow transplantation (BMT) and immunosuppressive therapies (IST) including antilymphocyte globulin became available. However, under supportive therapy alone, spontaneous remissions were observed in up to 20% of severe cases, reflecting the natural course of the disease. Therefore, in evaluating new forms of treatment, one has to keep in mind that remission is not necessarily response, and that final proof of utility of any new therapy still requires a randomized study design. Transition to leukemia or myelodysplasia was rarely observed if the initial diagnosis was accurate. The much higher incidence of leukemias in patients treated by IST, but not by BMT is probably due to the better life expectancy of patients at risk, rather than to a leukemogenic potential of IST itself. 'Outdated' therapeutic modalities, such as androgens or splenectomy, may still be justified as an adjuvant therapy in selected cases.