The relapses of 45 acute leukemia patients who underwent allogeneic bone marrow transplantation between April 1976 and February 1992 were analyzed clinically. The relapse rates of acute nonlymphocytic leukemia (ANLL) and acute lymphocytic leukemia (ALL) were 4/26 (15%) and 9/19 (47%), respectively. Although multivariate analysis could not be done, a high frequency of leukemia relapse was significantly associated with ALL, a younger age, history of extramedullary leukemia and blood-type identity. Chromosomal abnormalities at diagnosis, interval from diagnosis to bone marrow transplantation (BMT) and graft-versus-host disease (GVHD) prophylaxis were likely to be predictive of relapse. On the other hand, neither stage of leukemia at BMT, acute GVHD, sex, nor WBC count at diagnosis was a predictive factor. Eight of 10 relapsed patients achieved complete remission posttransplant, but the duration of remission was only 138 days on average. Four second BMT procedures for relapsed leukemia were carried out but were associated with many complications. However, one is alive well over 6 years after the second transplantation. There is a high treatment-related mortality following second BMT, but there is some possibility of long survival in some patients.