We performed an HLA-mismatched T cell non-depleted bone marrow transplant on a 53-year-old man with acute erythroleukemia that was highly resistant to conventional remission-induction chemotherapy. After conditioning that included total body irradiation, the patient received a two-HLA-antigen-mismatched bone marrow graft harvested from his sister using tacrolimus and methotrexate for graft-versus-host disease (GVHD) prophylaxis. He successfully established rapid engraftment accompanied by steroid-responsive GVHD localized to the skin. Although bone marrow samples on day 31 and day 66 disclosed a complete remission with full donor chimerism, the patient relapsed and died of pulmonary infection on day 154. There is evidence that tacrolimus is effective in alleviating GVHD. Selected patients who have partially mismatched related donors with less HLA disparity may benefit from tacrolimus-based T cell non-depleted bone marrow transplants because of the more potent graft-versus-leukemia effect that can be expected compared to transplants using T cell depleted inoculum.