Enzyme biocatalyst assemblies on electrode surfaces can be used to construct efficient membrane-less biofuel cells. The present study reports on the construction of biocatalytic oxygen electrodes based on the modification of porous carbon tubes with laccase and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate) (ABTS(2-)) as mediator, co-immobilized within electrochemically polymerized films. Porous carbon tubes are used as original conducting support for enzyme incorporation and for the transport of dissolved dioxygen solution via diffusive flow through the porosity. The activity of the laccase immobilized on the porous carbon support is determined. Performance of the biocathodes towards the reduction of dioxygen to water is demonstrated by chronoamperometry at +0.4 V vs. Ag/AgCl in citrate/phosphate buffer pH 3. Moreover, the current-voltage behaviour of the biocathodes show high current densities at pH 3 (a current peak equal to 280 mu A cm(-2) for the biocathode based on both entrapped laccase and mediator) and a low oxygen reduction overvoltage compared to platinum electrode.