The electrocatalytic reduction of nitric acid was studied at rhodized electrodes with low (10-25) roughness factor values in 1 mol dm(-3) H2SO4 supporting electrolyte, A simple logarithmic current vs. potential relationship was found for the cases where the role of transport processes could be neglected. Consequently, a simple charge transfer reaction could be considered as rate determining step. The inhibition of the reduction process by the adsorption of chloride ions was studied and it was shown that the potential and concentration dependent adsorption of Cl- species triggers potential oscillations under galvanostatic conditions. Similar oscillatory behaviour was observed under open circuit conditions in a hydrogen atmosphere, ie the oscillation of the mixed potential of two coupled reactions, the reduction of nitrate and oxidation of molecular hydrogen, takes place.