We applied an erythrocyte adhesiveness/aggregation test (EAAT) to a model of plasma exchange in individuals with familial and primary hypercholesterolemia. The significant (p < 0.0001) reduction in the concentration of fibrinogen by 56%, globulins by 48%, and cholesterol by 53% corresponded to the expected significant (p < 0.0001) reduction in the degree of erythrocyte adhesiveness/aggregation in the peripheral venous blood. By virtue of its being a real-time, simple, very-low-cost, and essentially bedside technique, the EAAT might have the potential of disclosing information of rheological relevance immediately before, during, as well as following apheretical procedures administered to patients with an impaired rheological profile.