The activity of Pt-Ir deposits on titanium for the reduction of the nitrate ion in 0.5 M perchloric acid was studied. The electrodes were characterized by SEM-EDAX, XPS and cyclic voltammetry. The activity of the electrodes for the nitrate reduction depended on the Pt-Ir ratio. Repetitive cyclic voltammograms produced an enrichment of the electrode surface with Ir and a decrease of the catalytic activity. A synergistic effect in the electrodes with low iridium content is discussed.