Nephrotic syndrome (NS) is associated with several disorders of hemostasis: thrombocytosis and platelet hyperaggregability; increased plasma levels of factors V and VIII, and of fibrinogen with blood hyperviscosity; decreased plasma levels of natural anticoagulants: free protein S, and antithrombin III compensated by increased levels of alpha 2-macroglobulin; lowered fibrinolytic activity. Intensity of hypercoagulability is related to the degree of hypoalbuminemia; however, the role of hypercoagulability in the increased incidence of thromboembolic events, including renal vein thrombosis, is not proved. Clotting disorders are due to urinary losses of anticoagulants or to increased liver synthesis of procoagulants stimulated by hypoalbuminemia. Moreover, changes in clotting factors levels may be due to intravascular thrombin formation (marked by increased plasma levels of fibrinopeptide A). During active phases of glomerulonephritides (GN) with NS, thrombin formation might in fact arise in glomeruli, following activation of the glomerular hemostasis system. Isolated glomeruli from human crescentic GN, rabbit nephrotoxic GN and rat HgCl2 autoimmune GN produce excessive amounts of procoagulant (tissue factor) activity (PCA). Sequential studies of the self-limited HgCl2 GN showed that glomerular PCA, proteinuria and glomerular fibrin deposits peaked concomitantly at the acme of the disease, suggesting that immunologically mediated glomerular damage had triggered the extrinsic coagulation pathway.