We investigated the graft-versus-myeloma effect (GVM) after allogeneic bone marrow transplantation (allo-BMT). Three patients with refractory multiple myeloma (MM) underwent related allo-BMT. Two of the patients showed disappearance of serum M protein 4 and 5 months after transplantation, respectively. One of them has remained in complete remission for more than 22 months after allo-BMT, with accompanying chronic GVHD. Two patients with relapse and disease progression after allo-BMT underwent donor lymphocyte infusion (DLI). Although one patient did not respond to DLI, the other developed acute GVHD after 4 weeks and achieved a 75% reduction in serum M protein. DLI did not produce severe acute GVHD or myelosuppression. These findings suggest the presence of a GVM effect. DLI may be an effective therapy for patients with MM who have relapsed after allo-BMT. Furthermore, non-myeloablative stem cell transplantation (mini-transplantation) for refractory MM should be investigated further as a potentially curative option.