The voltammetric behaviour of the Ru(NH3)(6)(3+/2+) redox couple was studied on Pt-TiO2-coated stainless steel and gold electrodes. The Pt-TiO2 coatings were prepared by metal organic chemical vapour deposition in the Pt:Ti composition range 1:10 to 1:80 atomic ratio. These electrodes behaved as ensembles of nanoelectrodes in which the Pt particles acted as active sites, whereas the TiO2 matrix was inactive. The voltammetric patterns recorded with all the electrodes in Ru(NH3)(6)Cl-3 solutions displayed quasi-reversible character. Peak current and peak-to-peak separation DeltaE(p) were examined as a function of scan rate. From the DeltaE(p) values the apparent heterogeneous kinetic rate constant of the Ru(NH3)(6)(3+/2+) redox couple was evaluated with the various electrodes. From these values the fractional surface covered by active Pt or inactive TiO2 was calculated. The active surface area was in all cases less than 0.06%. From X-ray diffraction measurements the Pt crystallite dimension was calculated to be 6 nm for Pt:Ti 1:10 ratio, and less than 3 nm for lower Pt:Ti ratios.