The cucurbitacins are of great interest because of the wide range of biological activities they exhibit in plants and animals. We studied the antioxidant properties of cucurbitacin B + E glucosides (cucurbitacin glucoside combination, CGC) and their direct free-radical scavenging properties, using ESR spectroscopy. Antioxidant activity was measured by the ability of the CGC to reduce preformed ABTS(center dot+) into its native form and to inhibit MDA formation during the oxidation of linoleic acid. In both methods, the CGC exhibited antioxidant activity in a dose-dependent manner as expected from antioxidants. Using ESR spectroscopy, we found that the CGC inhibited (OH)-O-center dot-dependent DEPMPO-OH adduct formation, O-2(center dot-)-dependent DEPMPO-OOH adduct formation, and the O-1(2)-dependent TEMPO adduct generated in the photoradiation-porphin system. The IC50 values were 0.38, 8, and 11 mM, respectively. Together, these data demonstrate that the CGC exhibits antioxidant properties, probably through the involvement of a direct scavenging effect on several free radicals. (C) 2007 Published by Elsevier Inc.