SummaryA review of experiments described in the literature discloses a lack of agreement about the influence of nutritional fats on blood coagulation and fibrinolysis. The numerous pertinent studies yielded contradictory results even if identical techniques were used.In our investigation, 17 normal subjects were given a breakfast containing 57 g saturated fats and one containing 54 g unsaturated fats. Before and 3 hrs after ingestion of the high-fat meal, blood was collected for determination of blood coagulation and fibrinolysis. There was no demonstrable difference between the two blood samples in terms of recalcification time of platelet-rich plasma in siliconized glass, euglobulin activity, fibrinolytic activity measured by lysis of plasminogen-poor and plasminogen-rich standard clots labelled with I131-fibrinogen, “activated fibrinolysis” (measuring the antiplasmin concentration) and the susceptibility to fibrinolysis of fibrin clots prepared in a standardized manner from fasting and hyperlipaemic plasma samples.In 6 normal subjects the experiments were expanded to encompass breakfasts with 118 saturated and 117 g unsaturated fats. After these high-fat meals, too, there was no demonstrable difference in recalcification time and in the various parameters of fibrinolysis.In order to establish whether atherosclerotic patients would show a different reaction to high-fat meals, the experiments were carried out also in 17 patients suffering from severe generalized atherosclerosis. These patients were given a low-fat breakfast, one with 57 g saturated fats and one with 54 g unsaturated fats. In this group, too, there were no demonstrable differences between the preprandial and postprandial data on blood coagulation and various parameters of fibrinolysis.