In the present paper, we report the emission of SO2 from 10 mM sulfite-treated birch (Betula papyrifera Marsh) leaves both in light and in the dark. The emission reaches maximum at around 60 min during treatment. In some leaves, maximum emission is noticed even after 5 to 10 min of initiation of sulfite treatment. It is also observed in the presence of 3-(3,4-dichlorophenyl)-1-1 dimethylurea (DCMU). However, the emission rates are higher in light than in the dark or in the presence of DCMU. This emission is not observed with sulfate-treated leaves.