The authors compare the results of allogenic bone marrow transplantations of relatives in patients with chronic myeloid leukaemia during the initial years of the transplantation programme 1991-1995 (group 1, 15 patients) with results achieved in 1996-1998 (group 2, 30 patients) and evaluate the effect of changes concerning supportive treatment and new diagnostic methods. The age median of group 1 was 35 years, the median age of group 2 46 years. In other parameters the groups were comparable. In 1991-1995 a high transplantation mortality by the 100th day was recorded (40% as compared with 17%) and a higher incidence of stage III and IV of the acute reaction of the graft against the host (GVHD) in group 1 (20% vs. 6%). In group 2 there was a higher transplantation mortality after day 100 associated with a more frequent chronic GVHD (0% vs. 16.5%). The total survival is insignificantly better in group 2 (60% in group 1 survive with a median of 58 months follow up and 67% of group 2 with a median follow up of 33 months). Group 2 comprises however older patients. In the improved early transplantation mortality participated new methods, a change of the posttransplantation immunosuppression, experience with care of transplanted patients and better collaboration with other medical disciplines. The authors did not observe a substantial effect of changes in the basic supportive treatment on results of transplantation. Late transplantation mortality associated in particular with a higher incidence of chronic GVHD could be in the authors' opinion reduced by longer administration of immunosuppression after transplantation, in particular in older patients.