Tissue damage as a result of oxygen radical generation may be involved in the pathogenesis of different diseases, carcinogenesis, aging and cell death. The inhibition of the proliferation rate of the immortalised human cell line ECV 304 after oxidant damage by oxygen radicals generated in a hypoxanthine-xanthine oxidase system and the protection provided by some selected flavone and flavonol glycosides as well as by caffeic acid and its derivatives was determined. The cytotoxicity of the reactive oxygen species was differentially influenced by selected flavonoids and seems to be determined by the pattern of substitution and by their lipophilicity. Apigenin and quercetin demonstrated the strongest effect on the inhibition of hypoxanthine-xanthine oxidase-induced toxicity (50 % restitution of the cells at a concentration of 0.36 microM and 3.1 microM, respectively). The beneficial effect of the flavonol glycosides rutin and hyperoside was weak, whereas flavone glycosides such as diosmin showed a better effect of protection.