Theory is presented for the interpretation of cyclic voltammetric and chronoamperometric measurements made on electrodes modified by being covered with an insoluble layer of a polymer containing electroactive pendant groups. It is assumed that the redox behaviour of the film is non-ideal and that the activity coefficients of the components of the redox couple can be reasonably modelled by regular solution theory. In this way non-ideal behaviour is interpreted in terms of a single 'interaction parameter'. It is found that a wide range of cyclic voltammograms for diverse polymier systems reported in the literature can be thus very satisfactorily described. We also report the synthesis of the novel polymer poly(4-vinyl-triphenylamine), PVTPA, and describe and interpret the behaviour of electrodes coated with this polymer during electro-oxidation in acetonitrile solution. Excellent agreement with the regular solution theory is found. Chronoamperometric data for the related polymer poly(4-vinyl-4′,4″-dibromotriphenylamine) is also reported and found to give good agreement with the theory. © 1988 Chapman and Hall Ltd.