Bone marrow transplantation was performed on a 15 year old girl with chronic myelogenous leukemia. The bone marrow was obtained from her younger sister, who was human leukocyte antigen haplo-identical but major ABO incompatible. As a result, the condition of pure red cell aplasia (PRCA) persisted over a long period of time. In order to overcome major ABO incompatibility, erythrocytes were eliminated from the bone marrow graft before transplantation, and methotrexate and cyclosporine (CsA) were used to prevent graft-versus-host disease (GVHD). Administration of erythropoietin proved ineffective. B19 parvovirus infection could not be detected during that time. Agglutinin titers decreased to less than fourfold in parallel with the recovery of erythrocytes. Reports on similar PRCA have been limited to cases of transplantation with ABO incompatibility and cases where CsA was administered to prevent GVHD. This suggests that ABO incompatibility and CsA might be related to the development of PRCA.