We have investigated silver diffusion driven by heating or irradiation with light in sulfur-rich Ge-S thin films close to the composition Ge20S80. Quantitative data regarding the amount of diffused silver has been gathered using Rutherford backscattering spectrometry. Thermal diffusion produces films with 35 at.% silver in the glassy matrix at saturation while photodiffusion forms a film with a maximum concentration of 43 at.% silver. Auger electron spectroscopy was used to establish that silver penetrates deeper in the chalcogenide film and the diffusion kinetics lacks an induction period when irradiation with light is applied. The shifts in the binding energies of the participating elements suggest that sulfur is in an oxidized state and is mainly coupled with germanium for thermal diffusion while in the case of photodiffusion it reacts predominantly with silver. (C) 2003 Elsevier B.V. All rights reserved.