AbstractIt is generally assumed that using high whole blood flow rates (WBFR), 80 ml/min, during peripheral blood stem cell (PBSC) collection on the Fenwal CS 3000 Plus blood cell processor will result in higher yields of mononuclear cells (MNC) than using lower WBFR (50 ml/min). To test this assumption, we retrospectively studied 129 PBSC procedures on 17 patients in a multiple myeloma protocol comparing MNC yield, as well as red blood cell (RBC), granulocyte, and platelet (Plt) content, of four average WBFR groups. Standard PBSC procedures were performed using modified procedure 1, interface offset 100, anticoagulant (AC) ratio of 11:1, small volume collection chamber, and a processing time of 4 hours. After correcting for AC volume used, the volume processed was divided by 240 minutes to obtain the average WBFR. WBFRs were separated into 4 groups of 40–49, 50–59, 60–69, and 70–79 ml/min.When compared to the highest flow rate group (70–79 ml/min), the three lower flow rate groups had significantly higher MNC yields of 16.2 ± 6.9, 13.1 ± 5.1, and 11.5 ± 4.7 × 109, respectively, as compared to 8.9 ± 6.1 ± 109MNC for the 70–79 ml/min group. There was no significant difference in granulocyte yield which ranged from 1.6 ± 2.1 to 4.5 ± 4.8 × 109.There were also significantly more RBC in the 70–79 ml/min group with 21.1 ± 2.2 ml than all three other groups with 16.2 ± 4.3, 16.6 ± 4.0, and 17.9 ± 4.2 ml, respectively, but high average WBFR collected significantly less platelets (0.6 ± 0.7 × 1011versus 1.9 ± 1.0, 1.5 ± 0.9, and 1.2 ± 0.9, respectively). Incidence of citrate reactions increased as flow rates increased, 6%, 18%, 30%, and 33%, respectively. We conclude that using a lower average WBFR during PBSC collection actually produced significantly more MNC, with equivalent granulocytes, less RBC, but more plate