A 46-year-old woman with Ph-positive CML received an unmanipulated BMT from an HLA-identical brother, conditioned with busulfan-cyclophosphamide. Five months after BMT, cytogenetic relapse occurred, and CsA was decreased and then discontinued. Mild acute GVHD occurred, but gradually improved with no immunosuppression. Forty days after CsA discontinuation, both cytogenetic and fluorescence in situ hybridization analyses showed a host-derived normal karyotype, 46,XX, and no evidence of leukemic cells or donor graft. The sustained host-derived hematopoiesis lasted for 2 years until sudden recurrence of CML. In this case, the discontinuation of CsA led to GVHD and also suppression of the relapsed leukemia, presumably by a 'specific' GVL effect. There was also graft failure. The observation that subsequent hematologic recovery was of host origin implies that, at least in this case, the GVL effect was not directed against normal host-type hematopoiesis.