Polyunsaturated fatty acids of the n-3 type (n-3 PUFAs) may offer some protection against ischaemic heart disease (IHD). Part of the evidence has been derived from our investigations on Greenland Eskimos. Through six expeditions to Greenland, we have studied Eskimos living on their traditional sea diet. We found favourable changes in lipids and lipoproteins, together with a reduced platelet reactivity in the Eskimos - findings of importance for their low incidence of IHD. In this survey we intend to review studies on the effects of an increased intake of n-3 PUFAs, focusing on lipids and platelets. We conclude that beneficial changes in general have been obtained. However, individual patients and patient groups likely to profit from supplementation with n-3 PUFAs need to be further defined. The optimum dose needs to be established, and the effect and safety to be documented by highly needed long term studies.