The toxic effects of excess Cu2+ and Zn2+ doses on growth of tomato seedlings were studied in a pot experiment with the measurement of fresh and dry biomass of the plants. The toxic effects of both elements were evaluated by measuring copper and zinc accumulations, glutathione S transferase (GST) and superoxide dismutase (SOD) activities in tomato plants. The doses were 0, 150, 300, 450, and 600 mg kg(-1) of copper as well as 0, 250, 500, 750 and 1000 mg kg(-1) of zinc, and two separate pot experiments were conducted for these metals. The experimental results demonstrated that the excess Cu2+ and Zn2+ applications inhibited the growth of tomato seedlings and diminished their biomasses. The applications increased copper and zinc accumulations in the shoots and roots in comparison to control treatments. The accumulations were markedly higher in the roots than those in the shoots. The excessive Cu2+ amounts caused significant decreases in the GST and SOD activities of the roots. However, the SOD activities in the shoots significantly increased with excessive Cu2+ doses. The excessive Zn2+ applications significantly affected the GST activities in the shoots and the SOD activities in the roots. Both enzyme activities in the roots decreased with excessive Cu2+ and Zn2+ applications. This study shows that GST and SOD activities in tomatoes may be used as sensitive indicators of copper and zinc toxicity.