The use of medium-chain triglycerides (MCT) in lipid malabsorption and lipoproteinlipase deficiency is well established. It is known from experiments in animals and humans that after parenteral administration MCT are rapidly hydrolyzed by lipoprotein lipase in plasma. The liberated medium-chain fatty acids are taken up independently of carnitine by mitochondria and oxidized to CO2 in extrahepatic tissues more rapidly than long-chain fatty acids. Medium-chain fatty acids are ketogenic, and consequently both medium-chain fatty acids and ketones are carnitine-independent energy carriers for different tissues. By simultaneously infusing glucose the risk of ketoacidosis can be minimizes. MCT in parenteral nutrition is a substrate which provides high-density energy without problems regarding osmolality or renal losses and with less interference to the reticulohistiocytes of the immune system. On the basis of these metabolic and functional properties MCT represent a valuable additional energy source in total parenteral nutrition.