Twenty-one patients, 18 with leukemia and three with severe aplastic anemia, were treated by allogeneic bone marrow transplantation. Acute graft-versus-host disease (GVHD) developed in 13 patients (62%), of whom nine (69%) had grade I, two grade II, one grade III and one grade IV. In all nine patients with grade I, elevation of the serum glutamic pyruvic transaminase level without an increase in the serum bilirubin level was observed, which suggested the presence of GVHD in the liver. All 11 patients with grade I and II responded well to therapy with predonisolone. Eleven (73%) of the 15 patients who survived for more than 100 days after marrow transplantation developed chronic GVHD. As signs of chronic GVHD, hepatic disturbances were observed in nine patients (82%), while exanthema, ophthalmic symptoms and oral mucosal symptoms were observed in seven (64%), six (55%) and four (36%), respectively. These symptoms could be well controlled by predonisolone combined with either azathioprine or cyclosporin A. Of the five deaths following the onset of chronic GVHD, three were due to interstitial pneumonitis, one to sepsis and one to relapse of the leukemia. Karnofsky's performance scores of five of the six surviving patients with chronic GVHD were 90%. Six patients with acute leukemia were still alive more than six months after marrow grafting. None of them have shown recurrence of leukemia. Five of these six had chronic GVHD.