In the present work, the catalytic activity and thermal stability of metallic Pd and Rh catalysts have been examined under different ageing atmospheres. It was shown that thermal treatment under the reducing and oxidising ageing atmospheres strongly affected catalyst stability in terms of surface areas and the chances observed in the chemical states of active metals. This was also related to catalytic activities that remained higher if laboratory scale ageing was carried out in the reducing ageing atmosphere. It was also found that engine bench and vehicle ageings correlated with the reducing laboratory scale ageing. Thermal deactivation of the aged catalysts is due to the collapse in surface area and the sintering of the Rh metal particles. Active metal particles may also be encapsulated in the sintered washcoat that is observed as a decrease in catalytic activity. (C) 2003 Elsevier B.V. All rights reserved.