Thin polymer films prepared from a series of tetrathiafulvalene (TTF) substituted polystyrenes in contact with acetonitrile solutions of tetraethylammonium electrolytes (TEAX, X=ClO4-, PF6-, CH3C6H4SO3-) have been studied using cyclic voltammetric, chronocoulometric and absorption photometry techniques. Reduction of the oxidized films, which proceeds via an intermediate mixed-valence state, was markedly affected by the nature of the supporting electrolyte anion. After allowance for uncompensated resistance, the reduction process could be treated by Fickian diffusion with anion dependent diffusion coefficients for charge transport through the polymer film. Chronocoulometric Cottrell slopes, nD1/2C, increased in the order: p-CH3C6H4SO3-<ClO4-<PF6-. © 1982 Elsevier Sequoia S.A.