The kinetics of charge transport in a poly-o-aminophenol-coated electrode was investigated by our measuring its ne response at the varying oxidation and protonation levels of the polymer. Impedance data are interpreted in terms of the diffusion-migration transport of both electrons and protons through the film. An observed change in coupled diffusion coefficients with the oxidation level corresponds with the potential dependence expected in the extreme case of electron-transport control, where electrons are transported by interchain electron hopping. A proportional relationship between the coupled diffusion coefficient and the proton concentration in solution implies that homogeneous electron transfer in the film is accompanied with proton transfer from the reduced sites to the oxidized sites of the polymer. The change in diffusion coefficient with pH can be attributed to a decrease in homogeneous electron-transfer rate constant with deprotonation of the polymer.