Twenty-seven patients above 40 years of age (range 40-55) with leukaemia underwent transplantation with haematopoietic stem cells from HLA-A, -B and -DR identical unrelated donors. They were compared to 69 younger patients, median age 23. In the older group, the diagnoses were acute myeloid leukaemia (AML) five, acute lymphoblastic leukaemia (ALL) three and chronic myeloid leukaemia (CML) 19. The corresponding figures in the younger patients were 21, 27 and 21, respectively. Conditioning consisted of cyclophosphamide (120 mg/kg) combined with 10 Gy total body irradiation. Immunosuppression was ATG or OKT3 for 5 days before transplantation and methotrexate combined with cyclosporin A. The probabilities of grades II-IV acute graft-versus-host disease (GVHD) were 23 and 21%, and the cumulative incidences of chronic GVHD were 64 and 50% in the older and younger patient cohorts, respectively. Overall, 3-year transplant-related mortality rates were 46% in patients > or =40 years of age and 32% in patients <40 years of age (P = 0.16). Three-year patient survival rates were 54 and 46% in the two groups, respectively. In patients with chronic phase CML, the corresponding figures were 67 and 68%, respectively. We conclude that patients above 40 years of age should be considered for transplantation with marrow from unrelated donors.