Graphene is a form of carbon material in which the carbon atoms are arranged in a two-dimensional honeycomb lattice. It is a promising candidate material for future electronic applications, including transistors, gas sensors, electromechanical devices and supercapacitors. We explore the applications of graphene in the field of bioelectroanalysis. This communication reports the influence of graphene surface groups on the bioelectrocatalytic activity of a model enzyme, laccase. A graphite oxide (GO) layer cast onto a glassy carbon electrode is subjected to electrochemical reduction. The surface morphology and composition is monitored with scanning electron microscopy, energy-dispersive x-ray microanalysis and infrared reflectance spectroscopy. The results indicate that carbonyl and epoxide groups are fully removed during electroreduction of GO although some OH groups remain after the electrochemical reduction. The OH groups can serve as redox mediators between laccase and the electrode. The surface composition studies reveal that the functionality and the reactivity of graphene can be optimised by electrochemical treatment. Laccase that is physically adsorbed on the electrochemically reduced GO catalyses oxygen reduction without a mediator at potential values up to +0.6V relative to an Ag/AgCl electrode. (C) 2013 Elsevier Ltd. All rights reserved.