Bone marrow transplantations in four patients (aged 8-28 years, median 27 years) with chronic myeloid leukaemia (CML) were performed from unrelated donors who were HLA-identical and MLC-negative. One patient was in the stage of refractory blast crisis, one in a chronic phase, and two in the second chronic phase. Conditioning treatment consisted of fractionated radiation and administration of cyclophosphamide; in the patients with their second chronic phase additionally etoposide. Cyclosporin A and methotrexate were administered to prevent graft versus host reaction. The patient in the blast crisis died on day 12 after transplantation of Candida pneumonia. The other three patients are still alive 128, 306 and 530 days, respectively, after transplantation, only a mild form of graft versus host disease having occurred. It is suggested that for patients younger then 50 years with CML in the chronic phase an unrelated donor should be searched for in the absence of a familial donor.