Secondary ion mass spectrometry (SIMS) was used to follow the evolution of RuO2/ZrO2 film electrodes. The coating mixtures with compositions 20% Ru + 80% Zr and 50% Ru + 50% Zr prepared on titanium supports from isopropanolic solutions of RuCl3 x 3H(2)O and ZrOCl2 x 8H(2)O precursors were heated to 200, 300, and 500 degrees C and analyzed by SIMS. Cl--concentration depth profiles as ion intensity versus sputtering time curves showed the hydrolytic conversion of the ZrOCl2 precursor in the outer part of the film at low temperature and noble metal content and a rather uniform distribution at elevated temperatures. Zr+/Ru+ ion intensity ratios showed the relative enrichment of ruthenium in the near surface region at 500 OC, while slight accumulation of zirconia at the surface was evidenced for both compositions in harmony with the results of emission FTIR measurements. No reaction between the oxide components or between coatings and support was identified in the systems investigated.