Allogeneic bone marrow transplantations were carried out between March 1983 and July 1985 in 31 patients aged 7 to 45 years (median 18 years). Acute lymphoblastic leukaemia in 1st to 5th remission was present in 8 patients, acute myeloblastic leukaemia in 1st and 2nd remission in 4 patients, chronic myeloid leukaemia, with various remission status, in 6 patients, 3 patients had severe aplastic anaemia and there were single cases of myelodysplasia and immature cell megakaryocytic myelosis. Transplantation was carried out during relapse in 8 patients with either acute myeloid or lymphoblastic leukaemia. Phenotypic HLA-identical mothers (n = 2) as well as genotypic HLA-identical siblings (n = 27), and in two cases HLA-non-identical mothers, served as bone marrow donors. In leukaemia patients the conditioning treatment consisted of fractionated total body irradiation and high dose cyclophosphamide or etoposide. Patients with severe aplastic anaemia received cyclophosphamide (4 X 50 mg/kg) and fractionated total nodal irradiation (total dose 8 Gy). 19 patients (61%) survived 14 to 605 days after bone marrow transplantation. 15 patients (48%) continue to remain in complete remission with Karnofsky indices of greater than or equal to 90%. Causes for death were infection (n = 3), interstitial pneumonia (n = 3), relapse (n = 3) as well as single cases involving acute graft-versus-host-disease, non-engraftment of donor marrow and veno-occlusive disease of the liver.