Twenty-three patients with aplastic anemia (18/23 with severe aplastic anemia) were treated with an immunosuppressive regimen consisting of cyclosporin A (CsA) and methylprednisolone (MP) (n = 7) or CsA, MP, and antithymocyte globulin (ATG; n = 16). Nineteen patients are alive with a follow-up of 4 to 25 months; three patients died of infections and one of a gastrointestinal hemorrhage. Within 3 months, improvement of hematopoiesis was seen in 14 patients (61%). First signs of a response after 23 to 88 days were followed by complete remission in eight patients, partial remission in three patients, and minimal improvement in three patients. Two of the patients with only minimal improvement were treated with a second course of immunosuppression and reached a complete remission and partial remission. Interestingly, remission proved to be dependent on the continued administration of CsA in four of five patients with partial or complete remission who could be evaluated up to now. Thus, CsA must have been effective in the induction and/or maintenance of remission in three patients. This observation is a very strong argument for the role of T cells in the pathogenesis of at least some cases of aplastic anemia and warrants further evaluation of the role of CsA in the treatment of aplastic anemia.