Plasminogen, a 92kDa glycoprotein, is produced by the liver and is present in plasma and extracellular fluids. Plasminogen is the inactive precursor of plasmin, a potent serine protease involved in the dissolution of fibrin blood clots. Plasminogen can be converted into the active plasmin by plasminogen activators urokinase (uPA), tissue plasminogen activator (tPA), factor XII-dependent components. The plasmin system has been implicated in a variety of physiological and pathological processes such as fibrinolysis, tissue remodeling, cell migration, inflammation, and tumor invasion and metastasis. Hereditary defects of plasminogen is a predisposing risk factor for thromboemboric disease. Plasmin dissolves the fibrin of blood clots and acts as a proteolytic factor in a variety of other processes including embryonic development, tissue remodeling, tumor invasion, and inflammation; in ovulation it weakens the walls of the Graafian follicle. It activates the urokinase-type plasminogen activator, collagenases and several complement zymogens, such as C1 and C5. It cleaves fibrin, fibronectin, thrombospondin, laminin and von Willebrand factor. Its role in tissue remodeling and tumor invasion may be modulated by CSPG4. Angiostatin is an angiogenesis inhibitor that blocks neovascularization and growth of experimental primary and metastatic tumors in vivo.