Two cases of paroxymal nocturnal hemoglobinuria (PNH) were treated with allogeneic bone marrow transplantation. With respect to rejection, they were in a high risk group, because of sensitization to the allo-antigen by multiple transfusions for several years. The sex of the donors differed from that of the recipients. The conditioning regimen consisted of cyclophosphamide, procarbazine and brsrlfan, and cyclosporin A was administered for the purpose of preventing graft versus host disease (GVHD). Engraftment was observed on the 16th and 15th day (WBC>1000/㎣). Acute and chronic GVHD were noted in both cases. The first case expired on the 184th day, because of chronic GVHD-associated sepsis and the second case is alive on the 529th day with 100% karnofsky status. Although our experience was limited, we could make the following conclusions: 1) Our conditioning regimen was sufficient to allow engraftment with total chimerism, which was confirmed by conventional clinical guides and the cytogenetic study. 2) Post-transplantation clinical courses were eventful with bacterial and viral infection, as well as chronic GVHD-associated morbidity or mortality, possibly because of previous massive transfusion and buffy coat, etc. 3) We observed hematuria in both cases and dissemination of viral warts, possibly due to reactivation of the papilloma virus. 4) PNH may be treated by bone marrow transplantation, with careful selection of the cases.