IAG gelatins were studied by the potentiometric titration with a silver electrode and ammonical silver nitrate solutions. It is found that IAG gelatins are classified into three groups according to their titration behavior. Effects of chloride, thiosulphate and adenine on the potetiometric titration curves were studied. Chloride has the most remarkable effect on the titration curve of gelatin solution, revealing itself as a bent or a plateau on the curve. It is found for IAG gelatins that there exist regressive relations between the initial potential and each of the thiosulphate and sulphur dioxide contents reported by other authors. Thiosulphate gives a maximum and minimum to the titration curve when the concentration of silver nitrate solution or the speed of the titration matches with the thiosulphate content of gelatin. Adenine seems to suppress somewhat the potential ascent along the titration curve as a whole.