A competitive inhibitor of serine proteases; inhibits human thrombin, urokinase, plasmin, and Factor Xa (Kis = 0.97, 1.3, 1.6, and 8.5 μM, respectively); inhibits bovine thrombin, Factor Xa, and trypsin, and porcine plasma kallikrein (Kis = 1.4, 2.1, 2.6, and 0.2 μM, respectively); inhibits clotting activity of human thrombin (IC50 = 10 μM); inhibits fibrin formation in rats (continuous infusion of 120 μmol/kg per hour)