1. Transport of L-homocitrulline, an amino acid which occurs in milk products, was studied with rat small intestine in vitro and from the human mouth in vivo. Absorption was partially dependent, in both systems, on the presence of sodium ions.
2. Metabolic inhibitors decreased L-homocitrulline uptake across the small intestine. Transport across the intestine did not occur against the concentration gradient but did show saturation kinetics.
3. The barbiturate, amytal, did not inhibit buccal absorption. Saturation kinetics were demonstrated.
4. Experiments were conducted with L-citrulline, or other amino acids, as possible inhibitors of L-homocitrulline transport. Results were compatible with Na+-dependent carrier-mediated uptake across the buccal mucosa. Active transport could be involved with the small intestine assuming that L-homocitrulline has a low affinity for the carrier system.