A new biocathode was built and tested. It consisted of bilirubin oxidase adsorbed on Vulcan XC 72 R and immobilized into a Nafion (R) matrix. The possibility of direct electron transfer between bilirubin oxidase and Vulcan XC 72 R was also demonstrated. The kinetics on biocathode were enhanced by including 2.2'-azinobis-3-ethylbenzothiazoline-5-sulfonic acid in the catalytic film. A first order reaction rate was observed for oxygen concentrations lower than 22%. A complete kinetic investigation of the system was shown. A biofuel cell test performed with this biocathode and Au70Pt30 nanoparticles as anode catalyst permitted to reach a power density of 170 mu W cm(-2) at a cell voltage of 0.6 V, which is superior to what can be obtained with the concentric design. (c) 2009 Elsevier Ltd. All rights reserved.