Tests conducted on dogs with a fistula of the pancreatic duct evidenced that various amino acids mixtures containing all the essential amino acids and differing mainly in the replaceable nitrogen dissimilarly act on the external secretion of the pancreas after their introduction into the blood. The most intensive secretion produces a mixture in which the replaceable nitrogen is represented by glycine alone. The mixture, one of its constituent is one of the dicarboxylic acids (glutamic) very poorly stimulates this function. At the same time, the action of all the studied amino acids mixtures is less pronounced than is the effect of the caseine hydrolysate. The commercial agent aminofusin L-600, containing all the essential amino acids with addition of polyols (xylitol and sorbitol) with no dicarboxylic amino acids in its composition, produces an intensive pancreatic secretion close to that caused by the caseine hydrolysate.