Immunosuppressive treatment according to four different regimens was administered over the course of eight years to 42 patients with aplastic anemia. With treatment protocols which included horse-ALG and horse-ATG, remissions were achieved in most patients, while with rabbit-ATG improvement was obtained, but only minimally, in 15 patients. First results with Cyclosporin A confirmed the effectiveness of this immunosuppressive agent in the treatment of aplastic anemia. The development of remission was, independently of treatment schedule, recognizable 23-88 days after onset of treatment. Often only partial remission was achieved. The long-term course, especially also survival, correlated with the results achieved within the first three months after onset of treatment. Recurrences occurred in 19% of patients but responded to repeated immunosuppressive treatment if preceded by complete remission. Side-effects to ALG and ATG occurred only during the first two weeks and were easily controllable. In some cases Cyclosporin A led to subjectively distressing side-effects.