Thin films made from the ionomer poly(ester sulfonic acid) Eastman AQ38 and the protein myoglobin (Mb) on pyrolytic graphite (PG) electrodes formed stable hydrated gels in water. While interactions between Mb and the ionomer undoubtedly control retention of the protein, Soret absorbance band positions suggest that Mb retains a conformation similar to the native state in the medium pH range. Cyclic voltammograms were reproducible for several months when Mb-AQ38 films were stored dry or immersed in aqueous buffer. The formal potential of Mb heme Fe(III)/Fe(II) in AQ films shifted -50 mV/pH between pH 4 and, 10, suggesting that one electron and one proton are involved in the electrochemical reaction. Square wave voltammograms of Mb in the AQ films were fit by nonlinear regression analysis using a model featuring dispersion of formal potentials. The effective electron transfer rate between PG electrodes and the iron heme of Mb in AQ38 films was comparable to those in surfactant films, but much faster than on bare PG in Mb solutions. Oxygen and trichloroacetic acid were catalytically reduced by Mb in AQ films with significant decreases in the electrode potential required.