In 1979 two patients with Philadelphia (Ph1)-chromosome-positive chronic granulocytic leukaemia (CGL) were treated with chemoradiotherapy and transplantation of bone marrow from their respective identical twins. Subsequently twelve patients with Ph1-positive CGL in chronic phase were treated with chemoradiotherapy followed by transplantation of bone marrow from their HLA-identical sibs. Two of the fourteen patients have died of complications of the transplant procedure; twelve patients are alive and well. All the survivors have normal or nearly normal blood counts; there is no evidence of recurrent leukaemia or Ph1-positive cells in any patient after follow-up periods ranging from 97 to 1112 days. Bone-marrow transplantation should be considered in the management of any young patient with CGL who has a suitable marrow donor.