A theoretical analysis of charge transfer in metal catalysts supported on a doped TiO2 carrier is presented. The development of the theoretical model is based on the metal-semiconductor contact theory and has been used to calculate the amount of charge transferred to supported metal crystallites, as a function of the electronic structure of the semiconducting support and the metal crystallite size. It is shown that TiO2, doped with higher valence cations, has unique properties which favor the transport of charge at the interface, The quantity of charge transferred is found to be as high as 0.5 electrons per metal atom for crystallites smaller than 2 mn or negligible for crystallites larger than 10 nn. The effect of charge transfer on the electronic structure of supported metal crystallites is discussed.