The study of the isotopic exchange of oxygen on oxides and metals affords additional information about the form of the oxygen bond at the surface of catalysts. As a result of high temperature treatment of oxides, there appears on the surface a form possessing the catalytic activity for isotopic exchange of oxygen at very low temperatures. One may suppose that under these conditions the exchange of oxygen proceeds through an intermediate formation of many-atom, strictly oriented, complexes. For oxides and metals having an equilibrium content of oxygen in the surface layer, the activity in a homomolecular exchange may serve as a measure of the reactivity of the surface oxygen and is well correlated with the catalytic activity in a series of oxidation reactions.