To indicate whether treatment of teeth with zinc chloride and potassium ferrocyanide would reduce dental decay by preventing proteolysis of the organic structures of the teeth, the effect of these agents was tested on trypsin and pepsin digestion of egg albumin ,whole dentin and decalcified dentin. Proteolysis of egg albumin in Mett tubes was enhanced by these agents. Normal dentin was not affected and decalcified dentin was digested to the same extent with or without treatment with ZnCl2 and K ferrocyanide. It was concluded that if any caries reduction is brought about by these agents it is probably the result of factors other than interference with proteolysis of dental tissues.