This paper describes a comparative study of laccase-based biocathodes containing different redox mediator species, namely porphyrin, ferrocene, osmium, and ruthenium complexes were immobilized onto carbon platforms entrapped in an electropolymerized polypyrrole matrix. Ferrocenium hexafluorophosphate (Fc), an Iron (III) porphyrin (FeTMPyP), a ruthenium complex [Ru(byp)(2)Cl-2], and an osmium complex [Os(byp)(9)Cl-2] were employed as redox mediators and have been characterized by cyclic voltammetry. Methanol/O-2 biofuel cell tests employing the biocathodes showed that they provide higher output power as compared with other systems. In the best conditions, the maximum power densities reached values around 81 +/- 4 and 71 +/- 3 mu W cm(-2) for [Ru(bpY)(2)Cl-2] and [Os(bpy)(2)Cl-2] at pH 4.5, respectively. (C) 2014 The Electrochemical Society. All rights reserved.