Electroplated mesoporous microspheres of Pt and Pt/Ru have been characterized at various stages of growth by scanning electron microscopy, surface area analysis, and for Pt/Ru, methanol, and CO oxidation response. Microscopy has indicated random, distributed sphere growth throughout the bulk of a carbon black film serving as a host matrix. The structures generally appeared to nucleate within the carbon film early and grew in diameter as deposition progressed, retaining a spherical morphology. Hydrogen adsorption/desorption on Pt samples indicated specific surface areas in excess of 45 m(2)/g, while carbon monoxide stripping on Pt/Ru samples indicated specific areas over 70 m(2)/g. Methanol oxidation and CO oxidation response is presented for Pt/Ru deposits that showed a slight enhancement in activity at lower loadings, i.e., smaller particle sizes. (c) 2007 The Electrochemical Society.