Background Nonmyeloablative allogeneic bone marrow transplantation has been used since the 1990s as a new hematological stem cell transplantation strategy for treating hematological diseases. The purpose of this study was to explore the graft-versus-leukemia (GVL) effects of donor lymphocyte infusions (DLIs) after nonmyeloablative allogeneic bone marrow transplantations, while assessing the declines in treatment-associated morbidity, mortality, and graft-versus-host disease (GVHD).Methods A total of 615 (H-2k) mice were injected with L615 tumor cells and received 500 cGy (60Coγ-ray) irradiation three days later, followed by an allogeneic bone marrow transplantation (allo-BMT). The allo-grafts consisted of 3×107 bone marrow cells and 1×107 spleen cells from BALB/C (H-2d) donor mice. Two days after the allo-BMT, the recipient mice were given 200 mg/kg of cyclophosphamide. Subsequently, recipient mice were infused with either donor spleen cells (2×107) on day 14 or 21, or donor spleen cells (5×107) pretreated with hydrocortisone and cyclosporin A (CsA) in vitro on day 14 post-BMT.Results The median survival time of mice that received DLI on day 21 and pretreated DLI on day 14 post-BMT was longer than that of controls and the day 14 DLI group (P