SummaryDifferent products are claimed to be thrombolytic. Some of them are activein vitro(fibrinoylsin, urokinase, streptokinase) and others would produce a fibrinolytic activity in the blood after injection (anticoagulants, nicotinic acid, pyrogens, etc.).In order to evaluate the therapeutic value of these drugs in the treatment of thrombo-cmbolic accidents four questions were studied for each product :1) activityin vitro;2) activity after administrationin vivo;3) side effects;4) dissolution of anin vivoclot.