Ionic conductivities determined from impedance measurements on electrochemically deposited films of polypyrrole and a polypyrrole + polystyrene sulphonate composite are used to distinguish between several morphological models of these materials. Both materials show ionic conductivities that depend strongly on potential and electrolyte concentration, thus discounting porous metal and homogeneous permselective polymer models. The ionic conductivities are strongly affected by changing the counter-ion, but the co-ion has little influence. It is concluded that these materials consist of permselective polymer aggregates which enclose pores containing electrolyte solution. Such materials appear to work well as permselective membranes because of the poor interconnectivity between pores.