Within the registry of the chronic leukaemia working party of the European Group for Blood and Marrow Transplantation, data were available from 103 patients with chronic myeloid leukaemia who were treated by bone marrow transplantation from haploidentical family members. The patients of median age 30 years were transplanted between 1983 and 1994 in 25 European centres. The overall probabilities of survival and leukaemia-free survival (LFS) at 5 years were 32 and 25%, respectively. In univariate analysis, two factors were identified which affected survival and LFS, ie the state of disease at the time of transplant and the degree of HLA disparity. Fifty-nine patients were transplanted in first chronic phase and the probability of survival at 2 years was 47%. Forty-four patients received their transplants for advanced disease and their probability of survival at 2 years was 25% (P = 0.004). Donor bone marrow was HLA-mismatched for 0-1 antigens in 54 patients (group 1) and for 2-3 antigens in 49 patients (group 2). At 2 years, the probabilities of survival for groups 1 and 2 were 46 and 27% (P < 0.02) and the probabilities of LFS were 43 and 24% (P < 0.03), respectively. Multivariate analysis confirmed the prognostic importance of the disease stage and of the HLA disparity. Patients transplanted in first chronic phase from a donor mismatched for 0-1 HLA antigens had a probability of survival of 52% at 2 years compared with 19% for patients transplanted in advanced disease stage from donors mismatched for 2-3 HLA antigens.