A 49-year-old man with myelodysplastic syndrome (MDS, RAEB in T) who relapsed following allogeneic bone marrow transplantation (allo BMT) was treated with infusions of donor buffy coat leukocytes. He sustained hematologic and cytogenetic remission, but severe graft-versus-host disease (GVHD) developed for which cyclosporin A and prednisolone were required. This therapeutic approach appears to be valuable for relapsed MDS following allo BMT as well as for chronic myelogenous leukemia (CML).