Horseradish peroxidase (HRP) and catalase (Cat) immobilized on edge-plane pyrolytic graphite (EPG) electrodes by methyl cellulose (MC). Both the hemoenzymes entrapped in the MC film undergo fast direct electron-transfer reaction, corresponding to hemeFe(III) + e --> hemeFe(II). The formal potential (E-0'), the apparent coverage (Gamma), the electron transfer coefficient (alpha) and the apparent electron transfer rate constant (k(s)) were calculated by performing nonlinear regression analysis of square wave voltammetry (SWV) experimental data. E-0' are linearly dependent on pH, indicating the electron transfer of Fe(III)/Fe(II) redox couple companied with the transfer of proton. The processes of catalytically reducing oxygen, hydrogen peroxide and nitric oxide by HRP and Cat entrapped in MC film are also explored. (C) 2004 Elsevier Ltd. All rights reserved.