Cyclic voltammetry and chronoamperometry have been employed for the preparation and characterization of noble metal electrode substrates modified with bismuth adlayers. The influence of bismuth ad-atoms on the electrocatalytic activity of the resulting platinum and gold modified electrode was investigated toward the electrooxidation of several sugar acid molecules in moderately alkaline medium. A direct comparative study regarding the catalytic activity between platinum and gold electrodes has been carried out in order to obtain useful information on the electrooxidation mechanism of sugar acids. It is found that different pre-adsorption processes of analyte on the platinum and gold electrodes were involved giving rise to different adsorption states in the oxide region and double region of potentials, respectively. The bismuth adsorbed species acts as a true catalyst on the direct electrooxidation pathway, providing the oxygen necessary for the oxidation of organic molecules adsorbed on the PtOx or Au sites in the oxide and double region, respectively. (C) 2003 Elsevier B.V. All rights reserved.