The influence of grapefruit juice intake on 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced colon DNA damage was examined using comet assay in F344 rats given 60 mg/kg of PhIP by gavage. F344 rats allowed free access to grapefruit juice for 5 days experienced clearly reduced DNA damage in the colon to a 40% level of control rats. The suppression of PhIP-induced colon DNA damage depended on the grapefruit juice concentrations. The serum concentration of PhIP was compared between grapefruit juice-pretreated and non-pretreated rats, but showed no significant difference in the areas under their concentration-time curves, peak values and half lives of PhIP. Furthermore, no obvious difference was found in the liver capacity for mutagenic activation of PhIP in Ames assay between grapefruit juice-pretreated and non-pretreated rats. These results suggest that grapefruit juice suppresses PhIP-induced colon DNA damage by a mechanism independent of PhIP absorption in the intestine.