Polymer supported catalysts prepared by the chemical deposition of Pt on chemically prepared poly(3,4-ethylenedioxythiophene)/poly(styrene-4-sulfonate have been studied as thin films in a Nafion matrix on carbon electrodes. Cyclic voltammetry has revealed that the Pt utilization is lower than for a commercial carbon supported catalyst, and this has been attributed to electronic isolation and poisoning of some of the Pt. Rotating disc voltammetry of oxygen reduction is essentially the same (similar n values, Tafel slopes, and real exchange current densities) at electrodes coated with polymer and carbon supported catalysts, with the current at any potential being approximately proportional to the active Pt area determined by cyclic voltammetry.