In order to meet the emission standards of 1980 and 1981, catalysts which can simultaneously reduce hydrocarbon, carbon monoxide and nitric oxide emissions will come into wide usage. Just as important will be fuel management systems that maintain tight control of the air/fuel ratio. Since the 1981 standards will be quite stringent, the effects of poisons such as lead, phosphorus and sulfur on the catalyst will be very important.A study was conducted to determine the effects of different amounts of sulfur dioxide on the activity of a Pt, a Rh catalyst and a fully formulated three component control catalyst.These catalysts were tested in the laboratory employing a synthetic exhaust, that which simulates real automotive exhaust. The catalysts were tested under various conditions that would be encountered during normal closed-loop operation. SO2 affects the catalysts differently under each of the above conditions. Under dynamic conditions the SO2 has very little effect on the catalytic activity, but some influence on oxygen storage, whereas the catalyst activity is extremely inhibited under fuel-rich and non-oxidizing conditions. These results correlate with those in the literature.