An 8-year-old male with idiopathic severe aplastic anemia was successfully treated with allogeneic bone marrow transplantation in June 1980. However, he had a severe aplastic recurrence on the donor marrow after 3 years of sustained and complete engraftment. An alternative immunosuppressive treatment was attempted as a second bone marrow transplantation could not be performed. Consecutive immunosuppressive courses with antithymocyte globulin, antithymocyte globulin plus ciclosporin A and ciclosporin A alone elicited good but transient responses. At present he needs uninterrupted ciclosporin A treatment to maintain normal donor hemopoiesis. An immune-related and persisting pathogeneic mechanism for the aplasia is suspected that responds to diverse and continuous immunosuppression.