The interactive effects of NO3 fertilization and salinity levels on leaf CO2 fixation, the dry matter accumulation, the proline and sugar contents in tomato shoots were determined in a greenhouse experiment using a well-controlled aerohydroponic systém. Under high salinity levels, increasing N fertilization from 5 mM NO3 up to 20 mM NO3 was ineffective in countering adverse effects of growth. Photosynthesis was inhibited as a result of both osmotic and specific ion effects. The high šalině concentrations stimulated the sugar accumulation in leaves, whereas the proline accumulation was primarily induced by increased NO3 levels.