Polycrystalline, boron-doped diamond (BDD) thin films were codeposited with Pt particles on either conducting Si(100) or Pt (poly) substrates. These dimensionally stable and corrosion-resistant electrodes consisted of well-faceted microcrystallites with dispersed Pt particles incorporated into the surface region. The metal particles were well anchored and ranged from 10 to 500 nm in diam. The active Pt metal loading was in the range of 200 to 400 ng/cm(2) (diamond electrode geometric area); however, the real catalyst loading was estimated to be near 0.1 mg/cm(2). Importantly, the Pt particles at the surface were in electronic communication with the current collecting substrate through the BDD matrix, and they were electroactive for underpotential deposition of hydrogen and oxidation of methanol. The dispersed Pt particles were extremely stable as no loss in the activity was observed after 2000 potential cycles between the oxygen and hydrogen evolution regimes in 0.1 M HClO4 (1-6 mA/cm(2)). Characterization results are reported.