A new, radiation-free, conditioning protocol, containing the original Hungarian mitobronitol (DBM) (DBM/ cytosine arabinoside/cyclosphosphamide) has been applied to 36 chronic myeloid leukemia (CML) patients followed by bone marrow transplantation (BMT) from HLA identical sibling donors between 1990-1997. In spite of some prognostically disadvantageous factors (half of them were above 40 years, 10 out of 36 patients were in accelerated phase, the disease history was longer than 2 years in average) the overall survival (30/36) and the leukemia free survival rate (26/36) were in accordance with the best international results. Transplantation-related toxicity was remarkably reduced in comparison to bone marrow transplantation performed by total body irradiation/cyclophosphamide (TBI/Cy) or busulphan/cyclophosphamide (Bu/Cy) conditioning protocols. Acute graft versus host disease was present in lower percentage (9/36) and the number of serious cases was only 2/36. Chronic GVH disease, generally known to be associated with antileukemic effect (GVL), occurred in 25 of cases. Early haematological relapse among the 34 patients with functioning graft occurred in 6 patients which rate is slightly higher than reported after TBI/Cy or Bu/Cy conditioning treatment. There was no relapse among patients transplanted within one year post-diagnosis and patients having CML with accelerated phase. The leukemia free post-transplant period was in association with the chronic GVH disease and full chimeric state.