1. To investigate the effect of different intraluminal concentrations on the mutual inhibitive effect of glycine and glucose on their jejunal absorption rates, eighteen convalescent Zambian African patients who had no clinical evidence of intestinal disease or of malnutrition were given constant intrajejunal infusions with those solutes either together or alone. A double-lumen tube perfusion system was used, and three solutions containing (A) glycine, (B) glycine and glucose, and (C) glucose, all of which were rendered iso-osmotic with sodium chloride, were perfused in random order at 12·0 ml/min. The concentration of glycine in the perfusing fluid was either 10 or 20 mm, and that of glucose either 100, 200 or 280 mm. By reference to polyethylene glycol 4000, the absorption rates of the solutes and water were calculated for a 30 cm jejunal segment.
2. At a glucose concentration of 200 or 280 mm, but not 100 mm, the mean rate of glycine absorption was decreased by approx. 30%. Glucose absorption rates were not significantly altered by glycine.
3. These observations, taken in conjunction with those from a previous investigation, are consistent with the view that there are two mechanisms for the jejunal absorption of glycine in man, one of which is inhibited by glucose at high intraluminal concentration.