Modifying effects of scordinin, a biological active component in garlic, on diethylnitrosamine (DEN)- and phenobarbital (PB)-induced hepatocarcinogenesis were examined in rats. Male F344 rats, 5 weeks old, were divided into 8 groups. After a week, groups 1 - 5 were given DEN (100 mg / kg body weight, i.p.) once a week for 3 weeks, whereas groups 6 - 8 received vehicle treatment. Group 2 was given 600 ppm scordinin-containing diet in the initiation phase. From 4 weeks after the start of experiment, groups 3 and 5 were fed scordinin, and groups 1 - 3 and 7 received drinking water containing 500 ppm PB. Group 6 was given scordinin diet alone throughout the experiment (24 weeks). The incidences of hepatocellular adenoma and carcinoma were significantly smaller in group 3 than those in group 1 (P < 0.005 and P < 0.05, respectively). The average numbers of liver neoplasms in groups 2 and 3 were significantly smaller than in group 1 (P < 0.01 and P < 0.0001, respectively). Glutathione S-transferase placental form-positive foci were also significantly decreased by scordinin treatment in the initiation or promotion phase. Scordinin significantly decreased the mean number of nucleolar organizer regions' protein (AgNORs) / nucleus in hepatocellular adenoma and carcinoma. AgNORs / nucleus in the non-lesional area was also significantly decreased by scordinin treatment during the promotion phase. These results suggest that scordinin is a promising chemopreventive agent for liver neoplasia.