Nine patients underwent allogeneic bone-marrow transplantation as treatment for chronic granulocytic leukaemia (CGL) during the accelerated phase, a point in the course of the disease when it has progressed beyond the stable chronic phase but before the onset of blast crisis. After bone-marrow transplantation, haematological and cytogenetic studies showed ablation of all evidence of leukaemia, successful engraftment, and persistence of normal haemopoiesis in all patients. In one patient severe myelofibrosis and osteosclerosis disappeared after bone-marrow transplantation. Two patients have died of complications related to graft-versus-host disease (GvHD) but with no evidence of CGL. In one patient haematological and cytogenetic evidence of recurrent disease developed after bone-marrow transplantation, and she survives in chronic phase. Six patients are free of disability, do not require transfusions, possess normal marrow chromosomes, and have persistent clinical and haematological evidence of complete remission from CGL. Intervention with allogeneic bone-marrow transplantation during the accelerated phase of CGL can eradicate the disease and can provide normal haemopoiesis with acceptably low early morbidity and mortality. The long-term efficacy of bone-marrow transplantation as treatment for CGL, and the most effective timing of the transplantation with regard to the course of disease have yet to be determined.