Electrochemical impedance spectroscopy (EIS) was performed on a system consisting of a thin polymer film that contained chromium salts on top of a 55% Al-Zn alloy layer on steel. Modification of the impedance behavior of the coated metal by the presence of chromium salts led to an extension of the electrical circuit generally used to model EIS data of deteriorating coating systems and was ascribed to a chemical alteration of the Al-Zn surface. The assumption of the presence of an inorganic surface layer underneath the polymer film explained the observed behavior. © 1999, NACE International.