The significance of thromboembolic complications in the etiology and development of cardiovascular diseases, such as ischaemic heart disease or myocardial infarction, is undisputable and well documented. It is commonly believed that intravascular thrombi may cause vessel narrowing and even lead to complete vessel occulsion. When encountering circulation, narrowing of vascular lumen, such as intravascular clots and platelet aggregates, is believed to result in thromboembolisms. Activation of the fibrinolytic system allows for the proteolysis of fibrin clots, the main components of vascular thrombi, and thus it may lead to vascular reperfusion. According to numerous data presented during the 15th Congress of the International Society on Thrombosis and Haemostasis (1995), the superior indications for the use of thrombolytic therapy are acute myocardial infarction and extensive pulmonary embolism. It is still more frequently used in the therapy of deep venous thrombosis and occlusions of peripheral arterial vessels. Treatment of cerebral stroke with thrombolytic agents is under experimental studies. The development of modern techniques in molecular biology, genetic engineering and biotechnology has led to the 'eruption' of quite new perspectives in thrombolytic pharmacology.