Composite polyaniline electrodes containing carbon nanotubes incorporated in the film and spontaneous Pt-Ru deposits as catalytic material for CO oxidation are reported. PANI films were electrosynthesized from a monomer acid solution with the addition of carbon nanotubes. Then, Pt-Ru deposits were obtained by immersing the polymeric film in H(2)PtCl(6) and/or RuCl(3) in HCl. Three series of deposits were prepared by either immersion in a solution containing both metallic ions during a fixed time or successive immersion in different solutions containing only one of the metallic ions during half of the established time and varying the sequence as follows: (i) first in H(2)PtCl(6) and then in RuCl(3) or (ii) first in RuCl(3) and then in H(2)PtCl(6). Adsorbed CO oxidation was studied by cyclic voltammetry in H(2)SO(4) solution. The electrodes were characterized through SEM and EDX. The different ways to obtain spontaneous Pt-Ru deposits are analyzed and their influence on CO oxidation is discussed. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.