Fifty patients with severe aplastic anemia (SAA) were treated with immunosuppressive regimens consisting of high-dose 6-methylprednisolone (HD-6MPr) followed by or given in combination with anti-lymphocyte globulin (ALG). Eighteen of 50 patients given one course of immunosuppression (IS) showed a response, as defined by self-sustaining peripheral blood counts, with no further need for transfusions; 8 of 27 and 2 of 7 patients given, respectively, two or three courses of IS responded. The overall response rate was 28 of 50 (56%). Seventeen patients died, 5 are alive but pancytopenic. The actuarial six-year survival is currently 65%. The following prognostic factors on admission were significantly associated with response to IS: 1) age over 30 years (P = .005), 2) a short interval from diagnosis to treatment (P = .03), 3) a small number of transfusions before treatment (P = .004). The sex of the patient, the number of transfusions before treatment, and the number of CFU-c from unfractionated as well as from T-depleted bone marrow had no significant influence on response to IS. After one month from IS, however, patients responding to IS had a significantly (P = .01) higher number of CFU-c on T-depleted marrow cells, compared with nonresponders. The present study confirms that over 50% of patients with SAA can be successfully treated with IS. Older patients, with a short interval from diagnosis to treatment and with rapid recovery of CFU-c growth on T-depleted marrow, have the best chance for autologous hematopoietic reconstitution.