The ability of nine synthetic eugenol-related compounds to scavenge O2- (generated by the hypoxanthine-xanthine oxidase reaction) was compared with their radical generation and cytotoxic activity. ESR spectroscopy showed that eugenol (4-allyl-2-methoxyphenol), 2-allyl-4-methoxyphenol, 2-allyl-4-t-butylphenol and 2,4-dimethoxyphenol efficiently scavenged O2- and produced radicals under alkaline conditions. 2-allyl-4-t-butylphenol showed the highest cytotoxic activity and DNA-synthesis inhibitory activity, possibly due to the hydrophobic radical reactivity. 2-allyl-4-methoxyphenol and 2,4-dimethoxyphenol showed higher antioxidant activity than 3-t-butyl-4-hydroxyanisol (BHA), but all these compounds showed comparable cytotoxic activity with each other. These findings suggest a possible link between the cytotoxic activity and radical generation/scavenging activity in eugenol-related compounds.