Tissue plasminogen activator (t-PA) is a protein involved in breaking down the blood clot. It is a serine protease found in the endothelial cells that line the blood vessels. Like any enzyme, it converts plasminogen into plasmin, the main blood clot lysis enzyme. Due to its lysis activity, t-PA is used in clinical medicine to treat cerebral embolism and thrombosis. Its use is contraindicated in cases of cerebral hemorrhage or head trauma. Plasminogen activator inhibitor 1 (PAI-1) is a glycoprotein, the primary inhibitor of t-PA and u-PA. It plays an essential role in controlling any excessive activation of fibrinolysis. It is present in plasma associated with vitronectin, in free form or associated with t-PA and in the alpha granules of platelets. Fibrinolysis corresponds to the solubilization of the fibrinous thrombus by plasmin, an enzyme originating from plasminogen adsorbed to fibrin. Plasminogen is activated by t-PA and u-Pa. PAI-1 by inhibiting plasminogen activators, it controls the degradation of fibrinous thrombus. A decrease in fibrinolytic activity promotes the occurrence of thrombosis, while excessive fibrinolysis leads to hemorrhages.