It was planned to investigate, by observing incorporation of [³H]$ thymidine into liver cells, the influence of Panax Ginseng upon hepatic DNA synthesis in mice that received ACTH. Thirty male mice (body weight: 18 ~ 20 g) were divided equally into the ginseng-ACTH and the saline-ACTH groups. Each animal of the ginseng-ACTH and the saline-ACTH groups received every day (subcutaneously) 0.05 m1/10 g body weight of ginseng extract (4 mg 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 0.01 unit of ACTH intraperitoneally one hour. after the last medication, and 1μCi/g body weight of [³H] thymidine after one more hour. Five animals, at a time, 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.1.). Following results were obtained: 1. The hepatic radioactive indices obtained from the saline-ACTH group 1, 10, and 24 hr after [³H] thymidine administration were 1.50±0.32, 2.16±0.33 and 2.79±0.31 (mean±S.D.), respectively. 2. The corresponding values obtained from the ginseng-ACTH group (2.71±0.22, 3.85±0.29, and 5.06±0.31) were significantly higher than the values of the saline-ACTH group. It is inferred from the above results that the ginseng tends to prevent reduction in hepatic DNA synthesis caused by ACTH administration.