During experiments designed to simulate the oscillations of composition observed upon the catalyst in a vehicle exhaust device, a Pt-Rh bimetallic catalyst supported on alumina was studied for three-way catalytic reactions under both stationary and cycling conditions, The results were compared with those obtained from employing platinum or rhodium metals supported separately upon alumina and indicated that during the operation of the oscillatory regime on the bimetallic catalyst there is a deactivation/activation mode associated with a fast redox process of the rhodium component which becomes partially oxidised to its inactive form, Rh2O3. Deactivation was not observed with platinum alone nor under steady feed conditions in the bimetallic case, The effect of this cycling deactivation is examined with respect to the temperature required to affect the bulk of the metals, its consequential reorganisation of the surface, and subsequent interaction with the oxygen.