The electrochemical properties of natural or synthetic ferruginous clays, nontronite, montmorillonite and saponite, were studied by cyclic voltammetry and impedancemetry. Clay modified electrodes were then tested for the reduction of hydrogen peroxide under different conditions: in acidic medium without redox mediator, in phosphate buffer solutions (pH 7 or 8) with a redox cation (methyl viologen, MV2+) or a biomolecule (hemoglobin, Hb) absorbed within the clay coating. In all cases, the presence of iron species in the octahedral lattice of the clays enhanced the electrocatalytic reduction currents of H2O2. The sensitivities of H2O2 calibration curves were 0.23, 54 and 132 mA/M cm(2) for Nont, MV2+-Nont and Hb-Nont modified electrodes, respectively. (C) 2009 Elsevier Ltd. All rights reserved.