Thirty-seven patients with chronic granulocytic leukemia have been treated with supralethal chemoradiotherapy followed by transplantation of bone marrow from HLA-identical donors. All patients showed engraftment, and the Philadelphia chromosome (PH1) disappeared in each case. Four patients had syngeneic grafts before blast crisis and are still alive; 2 are in remission not maintained by therapy, and 2 others are receiving chemotherapy after having relapsed in the chronic phase. Thirty-three patients had allogeneic grafts; only 2 received the grafts during blast crisis, and neither is a long-term survivor. Of the 13 patients who had grafts in the accelerated phase, 6 died of complications related to the transplantation, and 1 died after a myeloblastic relapse. Thus 6 patients are in unmaintained remission with a median follow-up of 13 months. Eighteen patients received grafts in the chronic phase. All 10 survivors are in unmaintained remission with a median follow-up of 14 months; in this group, no patient has relapsed. The granulocytic hyperplasia of the chronic phase can be more effectively ablated than established blastic leukemia. The mortality rate of transplant-related complications must be weighted against the typical rate of progression of chronic granulocytic leukemia. Although a longer follow-up period is needed for full evaluation, bone marrow transplantation may now be offered to patients in the chronic phase in an attempt to achieve long-term survival or cure of more than one-half of these patients.