The benefit of antithymocyte globulin in severe aplastic anemia in the pediatric age group was assessed. Four children received ten alternate-day courses of ATG (horse antihuman thymocyte globulin) as well as antihistamines and corticosteroids to minimize allergic reactions. The outcome of 19 other children with severe aplastic anemia who received ATG was also summarized. Combined data reveal that 12 of 23 have had a complete or partial response with residual thrombocytopenia and a probability of 48% survival one year from the start of ATG therapy as projected by life table analysis. Only one death has been recorded in the responding group. Response rate did not appear to be influenced by age, sex, etiology, initial blood count, interval prior to ATG therapy, or dose of ATG employed. Complications were minimal and included minor urticarial reactions and intermittent fever. Therapy with ATG should be considered in childhood severe aplastic anemia when bone marrow transplantation is not possible.