The electrochemical behaviour of glyoxylic acid has been studied by linear sweep voltammetry in acidic solutions. The oxidation of glyoxylic acid takes place mainly at potentials higher than 1.0 V/RHE, and has been found to be structure sensitive. At lower potentials, the formation of poisoning intermediates due to dissociative adsorption of glyoxylic acid is the predominant process. Two kinds of stable residues can be distinguished: CO-like species, and species which probably maintain the CC bond intact. The formation of these species depends on the applied potential and does not take place at open-circuit conditions. The oxidation of adsorbed CO takes place in the usual potential range for this species. Only a slight positive shift is observed, attributable to specific adsorption of glyoxylate anions which is stronger than that of bisulphate. The C 2 residues require potentials of about 1.0 V/RHE to be stripped oxidatively from the surface