From a study of the electrocatalytic reduction of nitrate on Pt and Rh electrodes over a wide pH range, HNO3 is suggested as the only reducible species in nitrate reduction on Pt, whereas both HNO3 and the nitrate anion are reducible on Rh. Rh is the more active catalyst of the two because it can activate nitrate even if no protons are available in solution. This is an important insight into the development of more effective nitrate reduction catalysts.