The lipids of rat milk, the contents of 9-- 10-day-old rat stomach and intestine, lymph, plasma, and liver were quantitated and their fatty acids were analyzed. Rat milk consists of 97% triacylglycerols, of which 35% of the fatty acids are of medium chain length (C8-C12). However, stomach triacylglycerols show a 25% reduction in medium chain fatty acids, which indicates preferential hydrolysis of medium chain fatty acids in the stomach. The intestinal lumen free fatty acid composition shows decreased medium chain fatty acids compared to long chain fatty acids, indicating preferential absorption of the former. Lymph was shown to contain a significant amount (approximately 22%) of medium chain fatty acids. The decreased content of medium chain fatty acids in vena cava blood compared to portal blood, and also the lower concentration of medium chain fatty acids in liver compared to blood, indicates preferential use of these fatty acids by the liver.