As illustrated in figure 1, hemostasis is a delicate balance between the coagulation system on one side, giving rise to the insoluble fibrin blood clot, and the fibrinolytic system on the other, which leads to dissolution of the clot. The center of both systems is a cascade of proteolytic enzymes, each activating the next, with the final proteases in each cascade, thrombin and plasmin, being the final effector molecules. Thrombin proteolytically cleaves soluble circulating fibrinogen to form the insoluble fibrin clot and plasmin cleaves fibrin into soluble degradation products¹. One of the primary regulatory points in the fibrinolytic system is thought to occur at the step of the plasminogen activators and their interaction with a specific group of inhibitors, the plasminogen activator inhibitors (PAI’s)². The two known, natural plasminogen activators in mammals are tissue plasminogen activator (tPA) and urokinase type plasminogen activator (uPA). tPA is found primarily in the vascular space while uPA is generally thought to be of more importance in the extravascular milieu. The primary PAI regulating uPA and tPA function is PAI-1. PAI-1 interacts with high affinity with both tPA and uPA, forming the typical stable serpin/protease complex^{1 , 3}. PAI-1 is unique among serpins in its lability, spontaneously transforming to an inactive or latent conformation with a tl/2 of approximately 90 minutes³. PAI-1 in plasma is predominantly bound to an abundant plasma protein, vitronectin which stabilizes PAI-1 in the active form⁴. Vitronectin is also present in the extracellular matrix of many tissues and it may serve to localize PAI-1 function to specific sites.