It is shown that the inhibiting action of sodium chromate on localized corrosion of aluminum exposed to a sodium chloride solution is mainly the result of polarization of the local anodes. Sodium chromate would be an even more effective inhibitor of corrosion in this case if it did not depolarize the local cathodes. In order to obtain dependable information on the mechanism of inhibitor action, the influence of the inhibitor on the behavior of the local cells must be studied. Polarization curves obtained by the use of currents from an external source are of value in studying the mechanism of inhibitor action only if information on local cell behavior can be derived from them. Two indirect methods of estimating the anodic and cathodic polarization curves of the local cells are described. These methods make it possible to obtain the local cell polarization curves without the necessity of locating or isolating the local anodes and cathodes. The practical application of these methods is limited by the assumption that the areas of the local anodes and cathodes are not altered by the application of external current. One of the two methods has additional limitations.