Modifications of the method of potentiometric titration with chromous chloride in the determination of tungsten and molybdenum have been described.The optimum experimental conditions are:(a) for tungsten,the concentration of HCl should not be less than 10 N and the tungsten concentration,not less than one milli-equivalent in 160 ml;(b) for molybdenum,the solution to be titrated should be 6 N in HCl and contain about one gram of KCNS in 80 ml.The addition of KCNS gives a sharp potential jump at the end-point.Under such conditions the titration may be carried out with non-compensation method at room temperature.The method has been applied to the determination of tungsten in wolframite and scheelite,and of molybdenum in molybdenite with results agreeing with those obtained by gravimetric methods.Such a determination may be accomplished within three hours.