The results of increasing blood flow capability in a modified system for plasma exchange with a rotating filter are reported. There were 742 treatments performed with the authors' original system (OS), limited to blood flows of 100 ml/ min, and 327 treatments performed with the updated system (US), allowing for blood flows of 150 ml/min. Blood flows for OS were 98 +/- 5 ml/min (mean +/- SD) vs 145 +/- 12 ml/min for US (p < 0.001). Plasma flows were 65 +/- 7 ml/min for OS vs 98 +/- 12 ml/min for US (p < 0.001). Plasma removal rate was 42 +/- 8 ml/min for OS vs 61 +/- 14 ml/min for US (p < 0.001). Mean treatment time was reduced from 76 +/- 23 min for OS to 52 +/- 17 min for US (p < 0.001) in spite of providing a similar amount of plasma removed per treatment (3,113 +/- 577 ml/Rx for OS vs 3078 +/- 797 ml/Rx for US; p = 0.48). Despite statistical significance, there were only small differences in filtration fractions (65 +/- 12% for OS vs 62 +/- 11% for US; p < 0.001) and patient hematocrits (34 +/- 6% for OS vs 33 +/- 6% for US; p < 0.001). In conclusion, modification of the OS to allow for increased blood flow has resulted in a substantial improvement in procedure efficiency and a clinically useful decrease in treatment time.