A simple, rapid and effective way was devised to determine an enzyme incorporated into electropolymerized conductive polymer films, by combining a thin-layer electropolymerization cell and the Bradford Coomassie colorimetric protein assay. The method has been successfully applied to the determination of horseradish peroxidase (HRP) entrapped into pyrrole and 3-alkylsulfonate pyrrole copolymer films.