Death from cardiovascular disease is rare among Eskimos. Haemostasis was investigated in twenty-one Greeland Eskimos and twenty-one age and sex matched Danish controls. Platelet lipid analysis demonstrated that a high consumption of omega-3 polyunsaturated fatty acids (such as cis 5, 8, 11, 14, 17-eicosapentaenoic acid [C20:5]) by Eskimos increased the proportion of omega-3 polyunsaturated fatty acids in the platelets. The Eskimos had a significantly longer bleeding-time due to a reduction in platelet aggregation. It is suggested that C20:5 in the platelets is converted by the vascular-wall tissue to an anti-aggregatory prostacyclin. Partial dietary substitution of arachidonic acid by eicosapentaenoic acid may reduce the incidence of thrombotic disorders, including myocardial infarction.