Since June 1977 eight patients with acute leukemia and three with chronic myelogenous leukemia (CML) have undergone cytoreductive therapy prior to a second allogeneic or syngeneic bone marrow transplantation (BMT). The median age was 24 years (range 7-49 years) and the median time to second BMT was 495 days (range 122-1887 days). Prompt hematopoietic recovery was documented in 11/11 patients and verified by cytogenetic analysis in 7/11. Early death (less than 100 days) was the result of sepsis in one, veno-occlusive disease in one and interstitial pneumonitis in two. Of seven patients who survived beyond 1 year, two patients subsequently died, one as a result of acute respiratory failure and one of leukemia relapse. Five are currently disease-free at 8+, 20+, 42+, 49+ and 72+ months after the second BMT. In this patient population which is at high risk for resistant disease and treatment-related toxicity, a second preparative therapy and BMT may offer a durable disease remission with tolerable toxicity.