Elevated plasma triacylglycerol (TG; triglyceride) concentrations, especially in the postprandial state, have been associated with an increased risk of coronary heart disease (CHD). Postprandial lipemia represents a complex series of reactions which occur following the ingestion of a meal containing fat and is associated with a number of adverse metabolic events including the production of atherogenic chylomicron remnants, the formation of the highly atherogenic small dense low density lipoprotein particles, a reduction in the concentration of the cardioprotective high density lipoprotein fraction and the activation of coagulation factor VII. Fish oils are a rich source of the long-chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid and docosahexaenoic acid. Long chain n-3 PUFA are effective hypotriglyceridemic agents, lowering both fasting and postprandial TG concentrations. There is a large body of evidence which shows that n-3 PUFA reduces plasma TG concentrations through reduced endogenous very low density lipoprotein production. This in turn may account for the reduced postprandial lipemic response following n-3 PUFA supplementation. However, this does not preclude a contribution of enhanced chylomicron clearance, which may be mediated through altered chylomicron size, structure or chemical composition, or altered lipoprotein lipase metabolism in terms of enzyme concentration, activity, or affinity for chylomicrons. However the precise biochemical nature of this effect remains to be established. The reduction of postprandial plasma TG concentrations by n-3 PUFA may partly explain why n-3 PUFA intake is inversely related to CHD mortality.