SummaryThe methods used to determine blood fibrinolytic activity are of two main types :a) Methods using patient’s blood (or some of its fractions) as substrate :—thrombolysis of diluted or undiluted whole blood, observed by simple inspection or measured by thromboelastography;—fibrinolysis of a clot formed from total or diluted plasma by observation of total fibrinolysis or progressive disappearance of the clot;—measurement of lysis-time of euglobulins.b) Methods where the substrate is not a component of patient’s blood but :—plasma or some other blood fraction from another individual;—casein (radioactive or not);—gelatin;—esters such as LEe, TAMe, etc.A simple method, which can be used in any laboratory, is presented. Used in conjunction with a rapid fibrinogen determination, it is useful for thrombolytic therapy or in the treatment of haemorrhage due to fibrinolysis.