1. A double-lumen perfusion technique has been used in man to study jejunal absorption of individual amino acids from an amino acid mixture simulating casein, and a tryptic hydrolysate of casein consisting of oligopeptides and amino acids.
2. Total absorption was greater from the tryptic hydrolysate than from the amino acid mixture. There was wide variation in the extent to which individual amino acids were absorbed from the amino acid mixture. This was decreased when the tryptic hydrolysate was perfused. Amino acids which were particularly poorly absorbed from the amino acid mixture were absorbed to a substantially greater extent from the tryptic hydrolysate.
3. The results suggest that the characteristics of absorption of amino acid mixtures do not represent those of absorption of the physiological products of intraluminal digestion, oligopeptides and amino acids.