Ion conductivity and permselectivity measurements were carried out on free-standing membranes of the conducting polymer polypyrrole. The membrane was prepared by electropolymerization on a microporous gold sputtered polycarbonate foil and stabilized by a Teflon frame which was mounted in a two-compartment measurement cell. In an asymmetrical three-electrode configuration the polypyrrole membrane was accessible to electrochemical oxidation and reduction (electron transfer), whereas in a symmetrical four-electrode configuration the ion transport through the membrane could be studied as a function of the oxidation state of the polymer under electron conservative conditions. It was found that polypyrrole exhibits an appreciable ion conductivity with pronounced anion permselectivity in the oxidized state, whereas polypyrrole modified by incorporation of long chain anions shows a distinct cation permselectivity in the reduced state. In both systems the ion conductivity is strongly affected by electrochemical oxidation and reduction of the polymer backbone.