The objective of our study was to obtain a predictor of the timing for peripheral blood stem cell (PBSC) collection using routine blood cell counts. For that purpose, we compared recovery kinetics of peripheral blood cells and CD34+ cells in non-Hodgkin's lymphoma patients who were given granulocyte-colony stimulating factor for PBSC collection after CHOP therapy. Peaks in the monocyte/WBC ratio and reticulocyte high fluorescence ratio (HFR) were observed 2 to 3 days prior to the peak CD34+ cell count. In addition, the appearance of immature granulocytes in peripheral blood correlated well with increases in CD34+ PBSC number. These findings suggested the peak monocyte/WBC ratio, HFR, and immature granulocyte count can be used as predictors of the timing for PBSC harvests.