It was planned to evaluate the influence of Panax Ginseng upon hepatic DNA synthesis in mice by observing incorporation of [3H] thymidine into the tissue cells. Thirty male mice(body weight: 18 ~ 20 g) were divided equally into the ginseng and the saline groups. Each animal of the ginseng and the saline groups received every day (subcutaneously) 0.05 m1/10 g body weight of ginseng extract (4mg of ginseng alcohol extract in 1 ml of saline) and the same amount of saline, respectively, for 5 days. On the 5th experimental day, all animals received 1 μCi/g body weight of [3H] thymidine intraperitoneally 2 hours after the last medication. Five animals, at a lime, of each group were sacrificed 1, 10, and 24 hours after thymidine administration, and their hepatic radioactivity was measured autoradiographically in terms of the % number of radioactive cells in 1,000 cell counts (Radioactive Index, R.I.). Following results were obtained: 1. The hepatic radioactive indices obtained from the saline group 1, 10, and 24 hour after [3H] thymidine administration were 3.23±0.23, 5.20±0.21, and 6.00±0.30 (mean±S.D.), respectively. 2. The corresponding values obtained from the ginseng group (4.22±0.33, 6.32±0.32, and 7.42±0.35) were significant higher than the values of the saline group. The inference from the above results was that the ginseng facilitated hepatic DNA synthesis.