A model considering the transfer of counter ions and solvent molecules has been presented to explain the complicated ion transfer in polymer films during electrochemical redox processes. The developed mixed ion transfer model is used to analyze the ion transfer behavior of poly(3,4-ethylenedioxythiophene) during doping and dedoping processes. The results indicate that both anions and cations are involved in n-doping as well as in p-doping processes. The behavior of different electrolyte ions is also studied. The developed model shows that solvent molecules are also transferred in conjunction with the ion transfer. (C) 2004 Elsevier B.V. All rights reserved.