Three groups of patients suffering from acute attacks or progressive multiple sclerosis (MS) are under investigation. First results revealed remarkable clinical improvements of patients with acute attacks in the groups treated by therapeutic plasma exchange (TPE) and immunoadsorption (IA). Only slight or no improvements were seen in the patients of the control group treated only with steroids. Plasma protein levels (IgG, IgM, IgA, fibrinogen) were considerably reduced in patients of the TPE group after each treatment procedure as expected. The same holds true concerning the total hemolytic capacities (THC) of the complement of the classic (CP) and the alternative (AP) pathway. On the other hand in the IA group only slight decreases of plasma proteins (about 20%) were observed, but the behaviour of THC's were quite similar than those seen in the patients of the TPE group. The THC decreases in both groups can be explained by removal of all complement factors (TPE group) or by the adsorption of single factors (IA group) of both complement pathways according to earlier in vitro investigations. The THC decreases in patients of both groups suffering from acute MS attacks could mean an "antiinflammatory" effect and could--at least partially--contribute to the clinical improvements of these patients.