It is well recognized that in subjects with cerebrovascular disease (CVD), changes in hemorheological properties may occur in about 50% of the patients. This paper concerns a study on microhemorheological perturbations of the erythrocyte membranes in a group of 20 RIA's patients, treated with Pentoxifylline. At the admission of the subjects to the study a trend to an increased whole blood viscosity and erythrocyte aggregation was associated to alterations of membrane fluidity analyzed by means of the fluorescent probes in the patients with respect to the controls. At the end of pharmacological treatment and wash-out, our data indicate a clear modification in erythrocyte membrane which results improved. Our results underline how the improvement of the erythrocyte membrane fluidity, induced by pentoxifylline, is a basic factor of blood flow in the microcirculation.