The photoemission derived electron binding energies (with respect to the Fermi level) of xenon atoms adsorbed on nonuniform metal surfaces are found to be sensitive to the l o c a lwork function of the respective adsorption site. As a consequence separated photoemission lines can be resolved corresponding to xenon atoms coexisting on differing surface patches. This effect makes photoemission of adsorbed xenon (PAX) a powerful tool to characterize heterogeneous surfaces on an atomic scale. Various examples are discussed to demonstrate the capability as well as the limits of this technique, such as the ‘‘titration’’ of surface defects and the determination of the surfacetopography of coldly deposited Agfilms.