SummaryThrombolytic agents are enzymes with proteolytic properties against fibrine and other proteins. These agents were since many years introduced in medicine for topical use. It is rather recently that very active thrombolytic substances have been purified and made available for parenteral use in man. Although the therapeutic use of the thrombolytica is being widely explored it is still difficult to define the indications. The first indication seems to be acute arterial occlusions not older than 48 hours and located in—or more distal to the brachial or iliac artery. Acute occlusions of the deep veins of the legs, acute arterial emboli and lung infarct are other indications which are better defined than myocardial infarction and cerebral thromboembolism. Many questions remain unsettled, particularly concerning the route of administration (intravenous or intraarterial), dosage (priming dose or continuous perfusion) and associated medication (hydrocortison, phenylbutazone, chlortrimeton, heparin, coumarin derivatives). The potential dangers, contraindications and antidotes are discussed. The numerous technical requirements for the use of thrombolytic agents are stressed as well. A proper selection of the patients and critical evaluation of the results are recommended.