Effects of ferulic acid (FA) known as a major constituent of rice bran or germ on 4-nitroquinoline-1-oxide (4NQO)-induced oral carcinogenesis were examined in 4 groups of male rats. The incidences of tongue carcinomas and preneoplastic lesions (severe dysplasia) in rats of the group given FA in the diet at a dose of 500 ppm after exposure to 4NQO for 5 weeks in drinking water at a dose of 20 ppm, was significantly lower on termination of the experiment (32 weeks) in the group with the carcinogen alone (P < 0.005 and P < 0.001 respectively). The results suggest chemopreventive activity for this phenolic compound on oral cancer. Modifying effects of rice germ on azoxymethane (AOM)-induced formation of aberrant crypt foci (ACF) were also examined, in 8 groups of male F344 rats. Numbers of ACF/colon, ACF/cm2 and aberrant crypts/colon in the group treated with AOM (15 mg/kg s.c. once a week for 3 weeks) and gamma-amino butylic acid (GABA)-enriched defatted rice germ (2.5% in diet) or the group with AOM and rice germ (2.5% in diet) were smaller than those of the group with AOM alone (P < 0.005). Exposure to defatted rice germ or rice germ during the initiation phase or the post-initiation phase also decreased incidences of AOM-induced large bowel neoplasms (P < 0.05). These results suggest chemopreventive potential for rice germ on colonic neoplasia.