Ascorbic acid (AsA) is one of the most important and abundantly occurring water-soluble antioxidants in plants. In order to assess whether exogenous application of AsA through the growing medium could modulate the antioxidant activities of red cabbage cotyledons in copper tolerance, a hydroponic experiment was conducted under greenhouse conditions. Seedlings subjected to 0 and 100 mu M CuSO4 solution were supplemented with 0 and 100 mg L-1 AsA for 10 days. Changes in the levels of several important parameters associated with oxidative stress, lipid peroxidation and antioxidant enzymes were measured. The effect of treatment with 100 mg L-1 AsA alleviated the inhibitory effects of Cu on antioxidant enzyme activities. The levels of the Cu-induced accumulation of active oxygen species, peroxidase activity and lipid peroxidation in seedlings treated with AsA were lower than in untreated seedlings. In addition, exogenous application of AsA increased endogenous level of AsA which had a protective effect on growth, pigment content and enzyme activities of red cabbage against Cu-induced oxidative stress. The data suggest that exogenous application of AsA may protect cells against oxidative damage and Cu toxicity.