The influence of transient changes in the exhaust gas composition on the low-temperature activity of a Pt/CoOx/Al2O3, catalyst and a commercial three-way catalyst has been studied. Periodic O-2 and CO pulses caused well-controlled perturbations in the composition of a synthetic car exhaust which was found to affect the overall performance of both catalysts. The presence of transients shifted the conversion starts of CO and propene as well as their light-off temperatures towards lower temperatures. The improved performance is suggested to origin from the combined effect of rich (CO) and lean (O-2) pulses that cause perturbations in the adsorbate composition on the active sites at temperatures below light off.