The activity of seven anthraquinones and four anthrones against nonenzymatic and enzymatic lipid peroxidation in vitro and their ability to scavenge free radicals have been studied. In nonenzymatic peroxidation in rat hepatocytes induced by /-butyl hydroperoxide, dithranol and anthrone were the strongest antioxidants, having IC50 values of 8 ± 1 and 24 ± μmol/l, respectively. Rhein (IC50 64 ± 2 μmol/l) and aloe-emodin (IC₅₀ 65 ± 3 μmol/l) showed the highest inhibitory activity against peroxidation of linoleic acid catalyzed by soybean 15-lipoxygenase. Anthrone (IC50 62 ± 2 μmol/l), dithranol (IC₅₀ 72 ± 1 μmol/l) and rhein anthrone (IC₅₀ 76 ± μmol/l) were the most effective radical scavengers of the diphenylpicrylhydrazyl radical. The antioxidant activities in hepatocytes and the radical scavenging activities were correlated, whereas the inhibition of enzymatic lipid peroxidation showed no correlation with the two other effects.