The electrodeposition of composites consisting of a non-stoichiometric tungsten oxide matrix and either RuO2 or IrO2 dispersed particles was investigated. These materials were then tested as electrodes for both reduction (hydrogen evolution) and oxidation (oxygen evolution) reactions in acid medium. The composite deposition was carried out by cyclic voltammetry, potentiostatic or galvanostatic electrolysis of suspensions of the RuO2 or IrO2 particles in two different media described as appropriate for WO3 deposition: (i) a colloidal suspension obtained from Na2WO4 and H2SO4 or (ii) a solution obtained by dissolving W powder in aqueous H2O2. All the deposited composites were found to catalyse the hydrogen evolution reaction but none was active in oxygen evolution, presumably due to an inadequate electronic conductivity of the matrix. Such a behaviour differs from that of Pt-containing tungsten oxide electrodes which have been described as suitable anodes for the oxidation of organics. (C) 2003 Elsevier Ltd. All rights reserved.