Eight patients with relapsed chronic myelogenous leukemia (CML) after allogeneic bone marrow transplantation (BMT) were treated with alpha-interferon and leukocyte transfusions of the bone marrow donor. Six patients responded with disappearance of leukemic cells (Ph1, BCR-ABL) and reestablished donor hemopoiesis. All six patients developed bone marrow hypoplasia and graft-versus-host disease (GvHD). Three of the six patients died of cerebral bleeding, infection and GvHD, respectively. The remaining three patients are alive and well at day 418, 677, 818 after leukocyte transfusions. Two patients relapsed with more advanced disease of CML after BMT and failed treatment. Donor leukocyte transfusions provide an effective therapy for patients with relapsed CML after BMT, but are associated with a high mortality due to bone marrow hypoplasia and GvHD.