A novel biocomposite electrode containing horseradish peroxidase (HRP) and zeolite co-immobilized on gelatin particles mixed with graphite was described. Comparing the composite (zeolite/graphite) and the biocomposite (gelatin/HRP/zeolite/graphite) electrodes showed that the latter presented an enhancement on the electrodes diffusion properties and, apparently, the enzyme co-immobilized with zeolite on gelatin was electro-active and functioned as mediator in the electro-oxidation of phenol. Various HRP/zeolite ratios were tested and the best result was obtained with the 1:100 m(HRP)/m(zeo) biocomposite electrode. These results confirm the existence of HRP-zeolite interactions, as previously observed in pseudo-homogeneous oxidation of phenol. (c) 2007 Elsevier B.V. All rights reserved.