Two commercial automobile three-way catalysts (RENAULT) of different configuration: (1) Pt, Rh active phase supported on ceria-promoted alumina washcoat, and (H) Pd, Rh active phase supported on zirconia-ceria-promoted alumina washcoat on cordierite supports, have been compared fresh and aged in a conventional automobile for 100,000 km in order to design and to adjust a catalyst ageing method suitable to imitate most relevant conditions of real tests. The characterization techniques were N-2 adsorption-desorption isotherms, powder X-Ray diffraction, elemental chemical analysis and activity tests. Activity tests were: (1) CO, NO and CH4 conversion versus temperature (from 120 to 500 degreesC), and (2) CO, NO and CH4 conversion versus the ratio between the concentrations of the oxidant and reducing species (lambda) at 500 degreesC (normal running temperature). Gas composition was close to conventional engine exhaust composition with and without water vapour. A strong deactivation has been observed as a consequence of thermal processes and loss of catalyst washcoat mainly for catalyst (II). Poison concentration along the catalyst has also been shown, however, its influence on catalyst deactivation was not as important as thermal processes were. (C) 2003 Elsevier Science B.V. All rights reserved.