To investigate whether the migratory ability of peripheral blood-derived CD34⁺ cells of patients undergoing autologous peripheral blood stem cell transplantation is related to the homing efficiency of these cells, the migration in vitro of these cells was determined and correlated with in vivo hematopoietic recovery. Large inter-individual differences of the in vitro migratory ability of the CD34⁺ cells were observed, ranging from 1.1% to 16.4% for spontaneous migration and 6.2% to 40.8% for SDF-1–induced (100 ng/mL) migration. Significantly faster hematologic recovery was observed in those patients who received transplanted CD34⁺cells that showed high spontaneous and SDF-1–induced migration in vitro (P < .05). Moreover, CD34⁺ cells from healthy G-CSF–mobilized donors exhibited significantly higher spontaneous and SDF-1–induced (P < .01) migration than CD34⁺ cells from patients mobilized with chemotherapy and G-CSF. The lower migratory capacity in vitro of patient-derived CD34⁺ cells was not due to lower expression of CXCR-4 but probably reflected decreased motogenic behavior of the cells. These results indicate that the migratory capacity of the cells is important for hematopoietic recovery. The data suggest that the engraftment potential of autologous stem cells is more or less impaired by treatment before or during the mobilization procedure and might possibly be restored by in vitro manipulation of the cells. In addition, an exponential relation between CXCR-4 expression and number of CD34⁺ cells that mobilized to the peripheral blood was found (P < .001), suggesting that CXCR-4 expression plays a role in the mobilization of CD34⁺ cells.