A synthetic lysine derivative with antifibrinolytic activity. Aminocaproic acid competitively inhibits activation of plasminogen, thereby reducing conversion of plasminogen to plasmin (fibrinolysin), an enzyme that degrades fibrin clots as well as fibrinogen and other plasma proteins including the procoagulant factors V and VIII. Aminocaproic acid competitively reduces the conversion of plasminogen to plasmin by plasminogen activators. It directly inhibits proteolytic activity of plasmin, but higher doses are required than are needed to reduce plasmin formation. Aminocaproic acid is used in the treatment of hemorrhage and prophylactically against hemorrhage, including hyperfibrinolysis-induced hemorrhage and postsurgical hemorrhage.