The reaction between SO2 and selenite ion is quantitative in 3.0-4.0 mol dm-3 acidic solution. This reaction has been used for the determination of atmospheric SO2. Air is passed through a selenite solution of known concentration for 10 min. The amount of selenite reacting with SO2 is determined by differential-pulse polarography. The SO2 Concentration is proportional to the change in selenite concentration. The proposed method has been applied to authentic air samples, and the results obtained were consistent with those of other methods.