In conclusion, graft-versus-leukemia is important to prevent leukemia relapse following allogeneic bone marrow transplantation. This beneficial GVL effect is at least partly mediated by T-lymphocytes and is greatest in transplants from HLA-nongenotypically identical donors. GVL is associated with the presence of GVHD, although preliminary studies suggest it may be possible to separate these two processes. Improvement in treatment results requires innovative effective therapies to enhance the direct antineoplastic effects of the preparative regimen or immune-mediated antileukemia mechanisms.