Epidemiological studies indicate that dietary saturated fats are implicated in coronary heart disease (CHD). Human prospective studies have shown that diets low in long chain saturated fatty acids and enriched in linoleic acid are beneficial in CHD-prevention. Experiments in animals have shown that such diets diminish atherosclerosis and the tendency to arterial thrombosis; they also lower the ability of platelets to aggregate in animals and in man. The mechanisms by which these diets produce these effects are not yet completely understood. Platelets and vascular prostaglandin-like substances may be involved as well as platelet membrane fluidity and platelet coagulant activities. On the basis of the available evidence, measures to decrease the intake of long chain saturated fatty acids (concomitant with an enhanced consumption of linoleic acid-rich products) are justified. Although certain marine oils may also have anti-thrombotic properties the possibility of undesirable side effects compels extensive investigation before their wide-spread use can be recommended.