A study of the coagulolytic balance as well as platelet aggregation was carried out in 64 nephrotic patients. The data were correlated, in a prospective attempt, with the clinical demonstration of thrombo-embolic events. Activating factors (factors I, VIIIc, VIIIr:Ag) were increased as well as certain clotting inhibitors, alpha-1-antitrypsin and alpha-2-macroglobulin. There was a platelet hyperaggregability in 31.5% of our patients. Thrombo-embolic complications occurred in six subjects (9%). The data of these six patients were compared with that of the other patients; no significant correlation were found between clotting abnormalities and thrombosis. Low level of ATm (less than 0.8 U.Fr) and severe hypoalbuminemia (less than 20 g/liter) were of no predictive value for the occurrence of thrombo-embolic events.