The potentiometric behaviour of films of zeolite toward aqueous phase cations is described. The stability of the potentiometric responses toward various analytes is used to diagnose the applicability of these materials for electroanalysis. Size selective behaviour with regard to cationic species is observed: cations with a crystallographic diameter exceeding that of the zeolite pores gave no measurable potential response. The zeolite films were formed using three distinct preparation routes: pressing discs of zeolite powder (for zeolite Y, zeolite A and mordenite), growing a free-standing membrane of zeolite (for sodalite) and using a secondary growth step to heal defects in pressed zeolite A discs. The approach presented is the first report of the use of coherent polycrystalline films, consisting solely of zeolite, in a potentiometric study.