Reactions of sulfur dioxide on perovskite oxides have been investigated from two distinct standpoints. First sulfur dioxide is a poison for reactions of carbon monoxide, nitric oxide and hydrocarbons (1–11). How to mitigate this poisoning and how to regenerate the catalyst is therefore of importance when designing pollution abatement catalysts for motor cars. However the reaction between sulfur dioxide and carbon monoxide, catalyzed by perovskites, itself may provide an important route for the removal of a major pollutant (12–16).