The aim of this paper is to review fibrinolysis laboratory tests of potential clinical usefulness. Since the activation of the fibrinolytic system may be responsible for several relevant pathological scenarios, it is crucial to know whether and to what extent fibrinolysis laboratory tests are useful for the diagnosis and therapy of individual patients. The plasma fibrinolytic system may be altered by deficiencies and/or abnormalities of some of its components. Few doubts remain concerning the possible role of fibrinolysis alterations in the pathophysiology of some hemorrhagic and thrombotic disorders. In hemorrhagic patients, laboratory tests may demonstrate the existence of increased plasmin activity and the presence of specific congenital defects leading to primary hyperfibrinolysis. Alterations of the fibrinolytic system should be looked for only in selected patients who have a history of venous thrombosis and negative results of initial screening tests.