Many clinical studies have evaluated the clinical efficiency of ticlopidine in vascular pathology and in few of these studies the plasma Fg level was determined as a biological parameter and not a primary end point. All these studies are heterogeneous because plasma Fg concentration have been measured using various methods, patients were included at various time after the acute event and were followed over a period of 1 to 24 months of treatment with ticlopidine, patients suffered from various pathology: peripheral arterial disease, cerebrovascular disease, diabetes or polycythemia vera. Despite the heterogeneity of these prospective studies, a general trend indicates a decrease in the plasma Fg levels by 10 to 25% with ticlopidine compared to placebo. This decrease in circulating Fg was associated with clinical improvement, and, when studied, hemorheological modifications (decreases in whole blood and plasma viscosities). The mechanism of ticlopidine action is discussed.