Fifteen patients suffering from severe aplastic anemia (SAA) (2 cases), acute leukemia (AL) (10 cases) and chronic granulocytic leukemia (CGL) (3 cases) received a bone marrow transplantation (BMT). The marrow donors were histocompatible siblings (14 cases) or isologous twin (1 case). Two patients with SAA are still alive, and the observation time is 11 Mo. and 48 Mo. In cases of AL, two of 5 patients received BMT during remission, and one of 5 received in relapse are alive, 19 Mo. 3 Mo. and 5 Mo. after transplantation. Of three CGL patients, only one who received syngeneic marrow is alive 27 Mo. after grafting.Acute graft-versus-host disease (GVHD) occured in 7 of 11 (67%) patients who received allogeneic marrow and were documented the engraftment. Two patients developed severe acute GVHD (grade III and IV) and one of them died due to GVHD. Transient and significant increase of serum IgE levels was found during acute GVHD or just before the onset of it in four cases.Chronic GVHD, resembling autoimmune collagen disease, developed in 5 of 6 long-term survivors. Four of them had experienced preceeding acute GVHD, one had a de novo late onset. Prednisolone plus azathioprine administered to three patients for treatment of chronic GVHD were effective. These 3 patients are now alive with Karnofsky scores of 90∼100%, 48, 19, and 11 Mo. after BMT.