Aseptically grown spruce seedlings were cultivated in a hydroponic system, where the roots were separated from the shoots by a gastight, silicone material. The plants were fumigated with four SO 2 concentrations (93, 190, 270 and 530 μg m −3) for nine weeks. Up to 270 μg m −3 of SO 2, an inhibition of nitrogen metabolism (enzyme activities of nitrate reductase (NR) and glutamine sythetase (GS) and nitrate content) in the shoot was compensated by a stimulation in the root, while nitrogen uptake was unaffected. Only the treatment with 530 μg m −3 of SO 3 decreased enzyme activities, nitrate content in both roots and shoots as well as nitrate uptake, and inhibited the growth of plants. Increases in the content of thiols and superoxidismutase activity are discussed in terms of SO 2 detoxification.