In non-sterile aqueous media, stainless steels (SS) may exhibit a non-stable behavior resulting from interactions between microbial species and passive film. They can induce the increase of the Open Circuit Potential (OCP) and they do so when they are organized in biofilms. Numerous studies have reported the catalytic effect of biofilms, involving enzymes, and their influence on the local physicochemical conditions related to their heterogeneous structure. To date, there are no enzymatic models able to mimic the interfacial processes: generation of oxidant species and specific physicochemical conditions. In our study, a SS-modified electrode based on a classical enzyme immobilization technique was conceived. Glucose oxidase (Gox) was immobilized in a polymeric him poured on SS surface to concentrate the enzymatic activity near the metal/polymer film interface. Electrochemical tests were performed to compare the effect of Gox when immobilized or free in the electrolyte. These experiments provided fine details about the reduction of both oxidants involved in the Gox-catalyzed reaction: H2O2 and O-2. The cathodic processes presented major differences between free and immobilized enzyme whereas the OCP ennoblement was found to be mainly due to an electrochemical effect of H2O2 in both cases. The immobilized Gox provoked a strong depletion of oxygen near the metal/polymer interface, indicating that the reduction current recorded was principally due to the H2O2 reduction. (c) 2008 Elsevier Ltd. All rights reserved.