In this retrospective study, we compared two systems, continuous flow (CF) (COBE Spectra) versus intermittent flow (IF) (Haemonetics V-50, M-30), in performance of therapeutic plateletapheresis ( T P N = 49 each) and therapeutic leukapheresis (TL: N = 29 each). Pre-and post-procedure cell reductions, specificity of removal, volumes removed, and incidence of adverse reactions were compared. Standard procedures with minor modifications, starch with IF only, and 180 minutes blood processing time were used. The CF system had a significantly lower percent reduction of platelets during TP at 43 2 17% than IF at 53 2 19%. However, no significant difference was found between CF and IF in percent reduction of white blood cells during TL with 49 f 16% and 42 ? 14%, respectively. The CF system had significantly less hemoglobin reduction (5 * 4% vs. 19 * 9%, respectively) and white blood cell reduction (13 * 15% vs. 27 ? 17%, respectively) for TP than IF and lower (not significant) hemoglobin reduction (9 t 8% vs. 12.4 2 8.2%, respectively) as well as platelet reduction (27 t 18% vs. 35 2 1996, respectively) for TL. C F also had significantly less volume removed than IF during TP (559 ? 97 vs. 883 2 304, respectively) and TL (7 10 * 134 vs. 1405 t 421 ml, respectively). Incidence of reactions was lower for CF than IF during TP (8% vs. lo%, respectively) and during TL (14% vs. 21%, respectively). Using our techniques, we found both the CF and IF flow systems were capable of adequately reducing cell counts for TP and TL; however, IF was significantly better in reducing platelet counts during TP. The CF system was more specific in its cell reductions as indicated by lower hemoglobin reductions, WBC reductions (TP), platelet reductions (TL), and volume removed. Reaction incidence was also lower for the CF system.