LEIS (low-energy ion scattering spectroscopy) measurements have been performed on fresh and used com. three-way catalysts (Pt/Rh/CeO2/g-Al2O3). The catalysts showed a significant decrease in the platinum surface concn. of approx. 50% after use in hydrocarbon oxidn. at cold-start conditions, and could be completely regenerated. The selectivity of LEIS towards the outermost at. layer allowed a one to one correlation between the surface Pt concn. as detected with LEIS and that obtained by kinetic modeling. This supports recent assumptions on selective deactivation. Conventional surface science techniques such as XPS, SIMS, or AES would have yielded ambiguous results, since their probing depths are not limited to the outermost at. layer.