This study was carried out to investigate the inhibitory effects of red ginseng extract on preneoplastic nodule formation in the rat liver using a rapid bioassay of hepatocarcinogenesis. Wistar male rats in test groups were fed diets containing 3.0, 0.3 or 003% of red genseng extract for 6 weeks after 2 week of dosing with diethylnitrosamine (DEAN, 200 mg/kg B.W., I.P.) or saline solution. The rats in the control groups were treated with DENA or saline alone. Three weeks after the beginning of the experiment, the two-thirds partial hepatectomy was performed on all animals. The inhibitory effects were investigated by measuring the number, total area and size of hyperplastic nodules enhanced by the 2/3 partial hepatectomy following induction with DENA. The results obtained were summarized as follows: 1. In general, the body weight gains of the rats fed diets containing red ginseng extract were higher than those of other groups.