SummaryIt has been found that a certain group of individuals fail to release, or release only very small amounts of plasminogen activator on exposure to a standardized stimulus (poor responders).For measuring the fibrinolytic response or capacity, venous occlusion of the limbs is a rather simple method, without potential sideeffects, which makes it suitable for routine clinical practice.The fibrinolytic activity or the blood obtained from the occluded arm proved to be 3 to 4-fold that of blood from the occluded leg, with a close correlation between both values.A strictly standardized technique must be applied to obtain reproducible results.A low response is observed with advancing pregnancy, in obesity, diabetes and in 38 % of patients with recurrent venous thrombosis. The response in Takayasu’s disease is poor or absent.Release assays with vasopressin (VP) and with a synthetic derivative (DDAVP), even moreactive than VP but devoid of side-effects, showed an impaired fibrinolytic response in patients with thrombotic disease. Further studies on the response to DDAVP in various clinical materials are desirable