Two new filtration systems (Fenwal CPS 10TM - PS 400 and Organon Teknika Curesis - M82) were evaluated and compared with two centrifugal cell separators (IBM 2997 and Haemonetics V50). 11 patients with auto immune diseases and dermatological diseases underwent 230 consecutive plasma exchanges. For the filtration systems, the average whole blood rate was 50 ml/min and the plasma separation rate was about 21 ml/min for a transmembrane pressure about 70 mmHg. The pre/post percent reduction and sieving coefficient were calculated for some plasma and blood components. A variety of laboratory studies was monitored to assess the efficacy of plasma separators, their biocompatibility and some yields. These results show that the 2 filters appear safe and efficacious but their modules are too simple and do not offer a great security (no transmembrane pressure control or no extracorporeal fluid balance). For a blood banker, IBM 2997 seems more interesting if we take in account its characteristics during plasma exchanges and the possibility which is offered to carry out cytapheresis procedures. But for a thrombopenic patient the filtration systems keep their advantages.