In May 1989, a 43-year-old woman with chronic myelocytic leukemia diagnosed in 1988 underwent a syngeneic bone marrow transplant (BMT), conditioned with cyclophosphamide-TBI while in chronic phase. Three years later, because of both cytogenetic and hematological relapse, she was treated with interferon-alpha (IFN-alpha) and hydroxyurea (HU) for 3 years. In 1994 while still in chronic phase, she was conditioned with busulfan-cyclophosphamide (BU-CY) and underwent a second syngeneic BMT. In 1996, following a further cytogenetic and hematological relapse, she was again placed on IFN-alpha and HU therapy for 13 months, when she was referred to our hospital in accelerated phase. In October 1997 following thiotepa, CY and anti-thymocyte globulin conditioning, she underwent an allogeneic BMT from her 1-Ag mismatched brother. She became Ph1 negative with full chimerism and normal hematological parameters; acute graft-versus-host disease (GVHD) grade 3 of the skin and chronic GVHD of the liver occurred. At 11 months follow-up she is in good clinical condition and with a Karnofsky score of 90%. The role of a graft-versus-leukemia (GVL) effect in securing and maintaining the complete remission is discussed.