A woman with lymphoblastic lymphoma was treated with combination chemotherapy. She subsequently became febrile while granulocytopenic and was given unirradiated granulocyte transfusions from normal, unrelated donors. She recovered, but 12 days later noted the onset of progressive skin rash, hepatic dysfunction, diarrhea and pancytopenia and, 22 days after her last granulocyte transfusion, died of gram negative septicemia. Histologic examination of multiple tissues including the skin, liver, and intestinal tract showed changes characteristic of acute graft-versus-hose disease (GVHD). Y-chromatin analysis of the patient's peripheral blood just before death indicated the presence of male cells. HLA typing of lymphocytes and skin fibroblasts from the patient and lymphocytes from the family and granulocyte donors was also consistent with engraftment of cells from one of the male granulocyte donors. This donor most likely was homozygous for one of the patient's halotypes, perhaps facilitating engraftment of his cells and subsequent development of transfusion-induced acute GVHD. Until more precise guidelines can be established, we recommend that all cellular blood products given to patients receiving intensive chemotherapy be irradiated with 1500 rad.