Summary:For 10 consecutive patients in our unit who did not show a significant rise in blood progenitor cells within 14 days following chemotherapy and G-CSF, we increased the G-CSF dose from 5 to 10 g/kg/day (n = 9) or from 10 to 15 g/kg/day (n = 1). As a result, there were significant increases in total yield as well as yield per apheresis of mononuclear cells, CD34 + cells and CFU-GM (P Ͻ 0.025, Ͻ0.01 and Ͻ0.005, respectively). After G-CSF dose escalation, six of the 10 patients had sufficient CD34 + cells for performing transplantation. These results demonstrate a dose-dependent response of progenitor cell mobilization by G-CSF when used in combination with chemotherapy. Moreover, increasing the dose of G-CSF as late as the third week of mobilization may still provide sufficient cell yield even with patients who did not show a significant mobilization with conventional doses of G-CSF. Keywords: stem cell mobilization; chemotherapy; G-CSF; CD34; CFU-GM With the discovery that the number of circulating hematopoietic progenitor cells dramatically increases during the recovery phase of myelo-suppressive chemotherapy, 1 various chemotherapy regimens were employed to mobilize peripheral blood stem cells (PBSC) for transplant. 2-4 However, the cytopenic phase following myelo-suppressive chemotherapy is often associated with significant morbidity or even mortality. 3,5 With the advent of hematopoietic growth factors (HGF), the use of combined chemotherapy and HGF in mobilizing PBSC results in a shorter cytopenic phase, reduction of infection risks and duration of hospital stay and enhances PBSC yield compared to mobilization with chemotherapy alone. 4,[6][7][8][9][10] Nevertheless, the dosages and scheduling of chemotherapy and HGF to optimize the cell yield, and hence the successful outcome of mobilization, remain to be studied.