The activity and isoenzyme content of superoxide dismutase (SOD) and changes in the leaf ultrastructure have been studied comparatively in chloroplasts of mesophyll and bundle sheath cells isolated from maize plants (Zea mays L.) grown in an artificial climate chamber at various concentrations of NaCl (0 mM, 50 mM, 100 mM, 200 mM). The SOD activity was found to increase in plants exposed to 50 mM and 100 mM NaCl, but at 200 mM NaCl it was partly inhibited. The study of the isoenzyme activity of SOD revealed Fe-SOD isoform, which intensity increased with enhancing salt concentrations. The analysis of the ultrastructures of mesophyll (M) and bundle sheath (BS) cell chloroplasts by electron microscopy showed that chloroplasts of M cells were sensitive,whereas chloroplasts of BS cells were tolerant to stress. At the high salt concentration (200 mM), a partial transition of the agranal structure of BS cell chloroplasts to the granal structure occurred