LEIS measurements have been performed on fresh and used commercial three-way catalysts (Pt/Rh/CeO2/gamma -Al2O3). The catalysts showed a significant decrease in the platinum surface concentration of approximately 50% after use in hydrocarbon oxidation at cold-start conditions, and could be completely regenerated. The selectivity towards the outermost atomic layer of LEIS allowed a one to one correlation between the surface Pt concentration as detected with LEIS and that obtained by kinetic modelling. 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 atomic layer.