A 15-year-old girl with Ph-positive chronic myelogenous leukemia in first chronic phase received bone marrow from her human leukocyte antigen matched brother. Twenty three months after bone marrow transplantation hematological relapse occured which was treated with two infusions of donor lymphocytes (DLI) (0.5x10(8) CD3/kg b.w./infusion). To enforce the graft-versus-leukemia effect (GvL), the first DLI was followed by administration of interferon-alpha (INF-alpha) 6x10(6) U/day for 30 days, whereas, after the second infusion INF-alpha was given at the same dose until hematological remission was achieved (80 doses). Minimal residual disease (MRD) was detected by conventional cytogenetics (Ph chromosome), fluorescence in situ hybridization (FISH) cytogenetics (BCR/ABL translocation) and reverse transcriptase-polymerase chain reaction (RT-PCR) Ecotropic virus integration site-1 (EVI-1 gene expression), whereas cellular chimerism was monitored by assessment of microsatellite markers PCR and Y-chromosomal DNA content FISH. When hematological remission was achieved the pancytopenia was observed and the cytogenetic and molecular investigations revealed only partial remission and mixed chimerism, however, with predominance of donor origin hematopoiesis. To diminish the myelosupressive effect of donor CD3 cells without switching-off the GvL effect, a low dose of cyclosporine A was given. Further observation revealed significant improvement of hematopoiesis with parallel gradual decline of MRD and increase of donor hematopoiesis up to complete chimerism. Graft-versus-host disease was not observed at any stage of the treatment.