The process of fibrin formation was systematically investigated in 25 patients with severe alcoholic cirrhosis. Results of functional tests are reported. A significant lengthening of the thrombin time was found which could not be completely attributed either to hypofibrinogenaemia or to an increase in physiological anticoagulants or to the presence of pathological antithrombins. A defect in fibrin polymerization was seen in the absence of significant levels of antipolymerizing agents. Indirect evidence pointed to an abnormal fibrinogen function. This was mainly suggested by the ‘polymerization curves’ of mixtures of normal and pathological plasmas and the changes in physico-chemical properties of the clot (optical and elastic properties; tensile strength). Altered synthesis in hepatocytes may lead to an ‘acquired dysfibrinogenaemia’ in the late stages of liver cirrhosis, although alteration of a normal fibrinogen molecule after secretion cannot be definitely e