Abstract Oscillatory phenomena occurring in the course of the reduction of nitric acid at a platinum electrode which were induced by the presence of chloride ions are presented. Both galvanostatic potential oscillations and potentiostatic current oscillations were observed. The influence of different parameters (concentration, current, potential) on the oscillatory behaviour was studied. By use of in situ radiotracer adsorption measurements it has been shown that the periodical changes of electrochemical parameters were coupled with those of chloride ion adsorption. Open-circuit potential oscillations were observed in a hydrogen atmosphere. This observation attests that the external electric circuit does not play a role in the generation of the galvanostatic oscillations. An attempt was made to give an explanation of the phenomena observed under galvanostatic and open-circuit conditions.