Intestinal absorption of sugars shows interaction with amino acids and vice versa. 2. The percentage of inhibition induced by a substrate depends on the type of substrate and the substance affected. 3. The mutual inhibition of monosaccharides and amino acids can be explained by five different hypotheses. 4. The most accepted hypotheses are the "allosteric interaction" and the "accelerated efflux". 5. From the results in the literature it is difficult to decide which of the two hypotheses is the more accurate.