Allogeneic peripheral blood progenitor cell transplantation (PBPCT) is increasingly being used to treat hematologic malignancies. However, the capacity of PBPC to maintain long-term hematopoiesis remains controversial. To add further information to this issue we studied the chimeric status in 12 patients receiving G-CSF-mobilized PBPC from HLA-identical sibling donors. All patients were conditioned with cyclophosphamide and total body irradiation. In six cases the apheresis product was partially T-cell depleted by counterflow centrifugation (n = 2) or the immunoadsorption biotin-avidin method (n = 4). The follow-up was longer than 6 months in five patients, with a maximum of 420 days. Molecular analysis of the engraftment was done using PCR amplification of short tandem repeats. Apparent complete donor chimerism was detected in all patients between 28 and 420 days after engraftment. This study indicates that full short-term engraftment is achieved in patients receiving allogeneic G-CSF-mobilized PBPC from healthy donors and suggests that this might also be true for long-term engraftment.