The electrochemical ionic exchange of polyaniline film-coated electrodes was studied in detail by electrogravimetry using an electrochemical quartz crystal microbalance. The influence of film thickness, electrolyte composition and potential sweep rate is discussed. The data obtained from these measurements establish the dependence of ion population inside the film on the degree of oxidation from −0.25 to 0.5 V (versus SCE). Analysis is made by calculating the relative contribution of anions and cations to the polymer electroneutrality from the electrochemical quartz crystal microbalance and electric charge data.