Cyclosporine A (CyA) was abruptly discontinued in an attempt to induce graft-versus-leukemia (GVL) effect following allogeneic bone marrow transplantation (BMT). It appeared that GVL effect was co-expressed with graft-versus-host disease (GVHD) in 2 of 4 patients and especially minimal residual disease was eliminated during GVHD in a patient with Philadelphia-positive acute lymphocytic leukemia. Subpopulation of cytotoxic T and natural killer cells increased significantly in patients with discontinuation of CyA. This finding suggests that GVL effect was increased following discontinuation of CyA. These results may provide a therapeutic strategy after BMT in patients with high-risk group for relapse of leukemia.