The effects of SO₂ and NO₂ on stress-related enzymes in Amaranthus hybridus [AH] and Lycopersicon esculentum [LE] were studied. The plants were exposed to SO₂ and NO₂ generated by chemical reaction in a chamber for one hour every day for three weeks. After exposure, chlorophyll content, ascorbic acid, catalase, proline content, superoxide dismutase and peroxidase from leaf samples were assessed. Catalase contents decreased (AH: 84.31 ± 2.56 and LE: 50.52 ± 1.74) in the plants relative to control samples, which showed appreciable retention (AH: 98.59 ± 4.70 and LE: 91.84 ± 7.12). Plants showed more reduction in peroxidase due to exposure to NO₂ compared to values obtained in plants treated with SO₂. Meanwhile, lower values of ascorbic acid and chlorophyll contents were obtained in plants exposed to SO₂ and NO₂ gases. On the other hand, proline content increased after exposure to the gases. Morphological disorders, such as leaf browning, chlorosis and shrinkage of leaves were also noticeable. So, it is apparent that plants exposed to elevated SO₂ and NO₂ gases did not exhibit sufficient capacity to counteract the stress imposed by these gases.