AbstractThe biochemical, regulatory, and physiological aspects of plasmin formation by the urokinase‐type plasminogen activator (uPA) is discussed and its involvement in cancer malignancy analyzed. Cell surface plasminogen activation has been shown to be essential in extracellular matrix degradation, basement membrane dissolution, and cancer invasiveness and metastasis in a variety of model systems. The ability of cells to produce plasmin on their surface depends on the presence of uPA and plasminogen receptors, and is the basis of the regulation of the plasminogen activating system in vivo. © 1993 Wiley‐Liss,