Polyaniline films in nonaqueous; media, mainly propylene carbonate and acetonitrile, are studied by using simultaneous potentiodynamic experiments with the electrochemical quartz crystal microbalance and electrochemical impedance spectroscopy. The role of ionic transport and solvent participation during redox reactions is emphasized to obtain information about all chemical species involved in the process occurring in the conducting polymer film. The contribution of each species (neutral and ionic) depends on both the chemical nature of the ionic salt and the solvent used. Quartz crystal microbalance results have shown that both cation and anion contribute to the electroneutralization process, and the participation of solvent molecules is related mainly to changes in the oxidation state of the polymer matrix. As propylene carbonate propylene (epsilon = 66.1) is a more polar solvent than acetonitrile (epsilon = 37.3), it produces a more pronounced swelling process.