Labelled oleic acid was introduced into the duodenum of chicks in which the pancreatic-duodenal vein and brachial artery had been cannulated, and blood samples were withdrawn. Similar experiments were performed in rats which had not been venously cannulated. In rat plasma, over 92% of the label was found in the triglycerides, whereas in the chick 64% of the label was in the triglycerides and 27-31% in the free fatty acids. In the rat, over 85% of the lipid label circulating in the plasma was found in lipoproteins with hydrated density less than 1.006, whereas in the chick only 25% of the label was in this fraction and the majority of label was found with density greater than 1.063. It thus appears that both release and transport of fatty acids from the intestinal mucosa in chicks differs from the rat.