Sixteen patients with chronic myelogenous leukemia (CML) underwent allogeneic bone marrow transplantation (BMT) when they presented with or developed objective signs suggesting acceleration of disease. Patients have been followed for a median of 515 days (range 216-806 days). Seven patients are alive from 319 to 732 days (median 538 days). Four patients are in complete remission 501-732 days after BMT. Three patients have developed cytogenetic evidence of relapse after BMT; however, these patients are alive and not dependent on therapy and have normal activity levels at 319, 515, and 550 days following BMT. Three additional patients have developed cytogenetic and hematologic evidence of relapse after BMT, progressed to blast crisis, and died. Six patients have died of other causes. Allogeneic BMT can eradicate the abnormal clone and provide normal hematopoiesis when performed during the accelerated phase of CML; however, this approach is associated with relapse and with relatively high mortality. The long-term efficacy of this approach and the relative efficacy of transplant during acceleration rather than during the chronic phase of CML have yet to be established.