Diamond Blackfan anemia (DBA) is a constitutional pure red cell aplasia of unknown etiology. There is laboratory evidence for an immune mechanism and most patients respond to corticosteroids. However the relapse and failure rate are high, and corticosteroids are associated with many short and long term side effects. Patients who do not respond or who do not tolerate corticosteriods require lifelong red blood cell transfusion and iron chelation therapy. Allogeneic bone marrow transplantation is an option for those with a related histocompatible donor, but this procedure is associated with high mortality and morbidity. Other therapies have been tried without general success. Occasional responses to either ATG or cyclosporine have been reported, but no study has used both ATG and cyclosporine. In other blood/bone marrow disorders of immune etiology these drugs have synergistic effects. We propose a Phase II study to explore the combined use of ATG and cyclosporine as a rational approach to the treatment of Diamond Blackfan anemia.