Electrochemical processes occurring at the interface platinumyttria-stabilized zirconia were investigated by cyclic voltammetry and potentiostatic current-potential curves, taken under steady-state conditions, in different mixtures of oxygen and nitrogen at temperatures between 300 and 600 degrees C. Point or paste electrodes were used. The exchange current of the rate-determining step of the oxygen reduction becomes very small below 500 degrees C. Therefore, the equilibrium of the oxygen electrode is no longer established. A layer of chemisorbed oxygen atoms is formed anodically on the contact surface of the point electrode, not by the dissociation of O-2 at the three-phase boundary. The shape of the cyclic voltammograms is discussed.