| Summary: | This study aims to evaluate the antioxidant potential of extracts of <em>Brassica oleracea</em> L. var. <em>acephala</em> DC. (kale) and several materials of <em>Pieris brassicae </em>L., a common pest of <em>Brassica</em> cultures using a cellular model with hamster lung fibroblast (V79 cells) under quiescent conditions and subjected to H<sub>2</sub>O<sub>2</sub>-induced oxidative stress. Cytotoxicity was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and glutathione was determined by the 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB)-oxidized glutathione (GSSG) reductase recycling assay. The phenolic composition of the extracts was also established by HPLC-DAD. They presented acylated and non acylated flavonoid glycosides, some of them sulfated, and hydroxycinnamic acyl gentiobiosides. All extracts were cytotoxic by themselves at high concentrations and failed to protect V79 cells against H<sub>2</sub>O<sub>2</sub> acute toxicity. No relationship between phenolic composition and cytotoxicity of the extracts was found. Rather, a significant increase in glutathione was observed in cells exposed to kale extract, which contained the highest amount and variety of flavonoids. It can be concluded that although flavonoids-rich extracts have the ability to increase cellular antioxidant defenses, the use of extracts of kale and <em>P. brassicae</em> materials by pharmaceutical or food industries, may constitute an insult to health, especially to debilitated individuals, if high doses are consumed.
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