The isoenzyme patterns of peroxidase (POD) and superoxide dismutase (SOD) were studied in the leaves of two different cultivars of wheat (Triticum aestivum cv. Chiarano and Mec) exposed to low concentrations of SO2 (35, 75, 120 nl l-1). After the SO2 treatments quantitative differences in the profile of the peroxidase bands were found, but no new isoforms were detected. An increase in the isoforms showing SOD activity was seen, this effect being more pronounced in cv. Chiarano than in cv. Mec. Our data show that the two wheat cultivars differ in their susceptibility to SO2 pollution, cv. Chiarano exhibiting a higher resistance.