Friction between the sliding tip of an atomic force microcope and a gold surface changes dramatically upon electrochemical oxidation of the gold surface. Atomicscale variations of the lateral force reveal details of the friction mechanisms. Stick-slip motion with atomic periodicity on perfect Au(111) terraces exhibits extremely low friction and almost no dependence on load. Significant friction is observed only abouve a load threshold at which wear Of the surface is initiated. In contrast, irregular stick slip motion and a linear increase of friction with load are. observed on electrochemically oxidized surfaces. The observations are discussed with reference to the amorphous structure of the oxo-hydroxide surface and atomic place exchange Mechanisms upon oxidation. Reversible, fast switching between the two states of friction has been achieved in both perchloric and sulfuric acid solutions.