Elevated plasma triacylglycerol concentrations have been associated with increased risk of coronary heart disease (CHD). In the past, the epidemiologic evidence about the causal role of triacylglycerols in CHD has not been well regarded, but recent prospective evidence shows that nonfasting plasma triacylglycerol concentration is a strong and independent predictor of future myocardial infarction. Elevated plasma triacylglycerol concentrations are associated with other CHD risk factors, namely reduced HDL-cholesterol concentrations and a preponderance of highly atherogenic, small, dense LDL particles. Plasma triacylglycerol concentrations increase after the ingestion of a fat-containing meal, and elevated postprandial triacylglycerolemia leads to a series of metabolic reactions that reduce HDL-cholesterol concentrations and promote the formation of small, dense LDL particles. The magnitude of the postprandial response is largely determined by fasting plasma triacylglycerol concentrations. Metabolism of plasma triacylglycerols also influences postprandial factor VII activation and the postprandial lipemic responsiveness to dietary cholesterol. Therefore, dietary factors that improve fasting plasma triacylglycerol concentrations must have a role in a healthy diet. Eicosapentaenoic and docosahexaenoic acids are n-3 polyunsaturated fatty acids (PUFAs) in fish oil that effectively reduce plasma triacylglycerol concentrations. Because n-3 PUFAs are effective at low doses (1 g n-3 PUFA/d), they provide a realistic option for the optimization of plasma triacylglycerol metabolism.