Four subjects were given test meals containing various concentrations of hydrochlorides of glycine, alanine, arginine, phenylalanine and tryptophan. The gastric contents were recovered after 20 min. The volume of the original meal recovered was assessed from the amount of marker substance aspirated. It was found that the slowing of gastric emptying of amino acid hydrochlorides was consistent with their action as weak acids. However, tryptophan and phenylalanine were slightly more effective than was predicted on the basis of their actions as acids.