The results are presented of allogeneic transplantation for 363 patients with acute non-lymphoblastic leukemia treated in Seattle from May 1973 through December 1985. The probabilities of surviving disease-free for 5 years for patients transplanted in first remission, in second remission, in untreated first relapse or in chemotherapy-resistant first relapse were 46%, 28%, 30%, and 21%, respectively. The corresponding probabilities of relapse within 5 years were 25%, 37%, 36% and 56%, respectively. Prognostic factors predictive of survival after marrow transplantation for patients transplanted in first remission included age, donor sex and the number of circulating blasts at the time of diagnosis. Acute graft-versus-host disease (GVHD) had a major adverse effect on survival, but chronic GVHD decreased the risk of relapse for patients transplanted in first remission.