Maca (Lepidium meyenii) is a plant from the Andes of Peru. Maca is used as a food for its nutritional value and ethnomedicinal properties linked to fertility and vitality. The purpose of this study was to evaluate the antioxidant activity of Maca. For all experiments an aqueous extract of Maca was used. The antioxidant activity of Maca was assessed by the inhibition of peroxynitrite, 1,1-diphenyl-2-picrylhydrazyl (DPPH), peroxyls and deoxyribose degradation. The cytoprotection capacity of Maca was assessed using macrophages (RAW 264.7) treated with peroxynitrite or hydrogen peroxide (H2O2). Catechins were quantified by reversed-phase HPLC. Addition of Maca extract (0.3-1 mg/ml) to peroxynitrite (300 μM) decreased peroxynitrite concentration by 15 and 41%, respectively (P<0.01). The IC50 for scavenging DPPH and peroxyls was 0.61 and 0.43 mg/ml, respectively. Deoxyribose protection by Maca (1-3 mg/ml) against hydroxyl radicals was in the order of 57 and 74%. Maca (1 mg/ml) protected RAW 264.7 cells against peroxynitrite-induced apoptosis (P<0.01), and increased ATP production in cells treated with H2O2 (1 mM). The concentration of catechins in Maca was lower than in green tea (2.5 mg/g vs 145 mg/g). Collectively, our results indicate that Maca has the capacity to scavenge free radicals and protect cells against oxidative stress. Copyright © 2002 Elsevier Science Ltd.