A 41-year-old female patient with AML, who relapsed after an allogeneic BMT from her HLA-identical sister, was treated by a donor leukocyte transfusion (DLT). Thereafter, bone marrow aplasia accompanied by the disappearance of leukemic blasts following the GVHD was observed. The patient died of chronic GVHD with respiratory muscle involvement 19 months after the DLT. Although the DLT was considered helpful in suppressing the proliferation of the leukemic cells, it might also have caused the severe GVHD observed in this case. Efforts to separate the lymphocyte clones responsible for GVL from those for the GVHD thus appear to be necessary for the further development of the therapeutic approach, so-called DLT.