A number of natural polyphenols (chlorogenic acid (9), cordigol (1 l), cordigone (12), danthrone (l), 1,5-dihydroxy-3-methoxyxanthone (Z), eriosematin (7), flemichin D (S), frutinone A (6), mangiferin (4), quercetin (5), 1,3,6,7-tetrahydroxyxanthone (3) and verbascoside (10)) were investigated for their redox properties using cyclic voltammetry. The antioxidant properties of these compounds were also examined in two models, namely lipid peroxidation in rat synaptosomes and AAPH-mediated oxidation of serum albumin. Compounds with a catechol group (9,4,5,3 and 10) were oxidized below 0.4 V and inhibited lipid peroxidation with IC,, values between 2 and 8 FM. Compounds having one or more isolated phenolic groups and showing an oxidation potential between 0.45 and 0.8 V (11,12 and 8) inhibited lipid peroxidation with ICs0 between 7 and 9 p ~, except 2 (0.45 V), danthrone (0.96 V) and eriosematin which showed no or modest antioxidant activity. Some of the investigated compounds also protected albumin from oxidation, but no structure-activity relationship was apparent, suggesting that other factors beside redox potential influence this activity. ') 0 . 0 7 ~ phosphate buffer (pH 7.4)/EtOH 1:l ( v / w ) ; working electrode: GC YS. Ag/AgC1/3~ KCl; auxiliary electrode: GC; sweep rate: 100 mV sC'.