Healthy seeds of black gram (Vigna mungo cv. PU-19) were surface sterilized with 0.01% HgCl₂ and grown in pots with a diameter of 23 cm. In each pot, one healthy seedling was left after 10 days of germination. The plants were exposed to 0.0 (control), 0.05, 0.10, 0.15 and 0.20 ppm of SO₂ for 3 h on alternate days for 56 days in the exposure chambers. All growth parameters, i.e. root length, root dry mass, number of nodules per plant and nodule dry mass, decreased with increasing concentration of SO₂, indicating its toxic effect on the plant and soil bacterial population.