The effects of ileal infusion of Intralipid on the time required for a radiolabeled liquid starch meal to empty from the stomach and reach a point in the ileum that was 230 cm from the teeth and on the ileal flow rates and the degree of carbohydrate absorption were measured in 5 normal volunteers. The subjects were intubated with a four-lumen polyvinyl tube. Studies were carried out on consecutive days in random order. Infusion of fat into the ileum (a) slowed the transit of a liquid meal through the stomach, (b) delayed the arrival of the liquid meal in the ileum and increased its residence in the upper small intestine, (c) reduced the average flow of digesta through the upper small intestine and altered the pattern of flow, (d) reduced the volume of the meal entering the ileum, and (e) reduced the degree of carbohydrate absorption in the upper small intestine. These results suggest that the presence of fat in the ileum may have a profound influence on the digestion and absorption of a meal.