Erythroid engraftment after non-T cell-depleted allogeneic bone marrow transplant (BMT) is reviewed in 112 patients treated for chronic myelogenous leukemia (CML). Twenty-two of 76 evaluable patients were transplanted over a major ABO-mismatch compatibility barrier. These patients showed an increased delay in erythroid engraftment and in time to red blood cell transfusion independence when compared with ABO-identical or minor mismatched recipients. No difference in granulocyte or platelet engraftment was evident. Erythroid engraftment usually occurred spontaneously without specific intervention. One patient was found to have erythroid hypoplasia at day 201 after BMT, despite therapy with intravenous immunoglobulin and high-dose erythropoietin. An anti-A titer of 16,000 was documented. This patient was successfully treated with an aggressive course of 18 plasmapheresis procedures and with donor-type plasma replacement. Delayed erythroid engraftment is common after non-T cell-depleted major ABO-mismatched BMT in CML, but rarely requires intervention other than transfusion support. Rare cases of refractory erythroid aplasia may be treated without additional immunosuppression by aggressive plasma exchange with donor-type plasma.