Oxide-supported metals constitute one of the most important classes of heterogeneous catalysts, and for this reason they have been investigated by many techniques: adsorption isotherms, LR of chemisorbed molecules, electron microscopy, EXAFS, etc. However, the fact that they have been studied by so many methods proves that no one technique is totally satisfactory. The physical and chemical properties of sufficiently small particles, in particular their magnetism, must depend on their size, whence the idea of using NMR to study them. Because of the theoretical and technical difficulties associated with the NMR detection of metals, and especially since only a few can be detected, NMR work has been mainly devoted to the indirect study of metallic properties, by the intermediary of easily detected chemisorbed phases (H-1, C-13) Or Of physically adsorbed probes (Xe-129). However, when the metal can be detected directly (mainly Pt), it is possible to relate the form of the NMR spectrum to the dispersion of the metal and to calculate the electron density of states at the Fermi level.