It was planned to investigate, in mice that received ACTH, the influence of Panax Ginseng upon DNA synthesis of submandibular gland by observing incorporation of $[^3H]$ thymidine into the tissue cells. Thirty male mice $(body\;weight:\;18{\sim}20\;g)$ were divided equally into the ginseng-ACTIH 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 $1\;{\mu}Ci/g$ body weight of $[^3H]$ thymidine after one more hour. Five animals, at a time, of each group were sacrificed 1, 10, and 24 hr after $[^3H]$ thymidine administration, and the radioactivity of cells in their mandibular gland was measured autoradiographically in terms of the % number of radioactive cells in 1,000 cell counts (Radioactive Index, R.1.). Results obtained were as follows: 1. The radioactive indices obtained from submandibular gland of the saline-ACTH group 1, 10 and 24 hr after $[^3H]$ thymidine administration were $15.2{\pm}0.32,\;20.1{\pm}0.30,\;and\;24.5{\pm}0.52(mean{\pm}S.D.)$ in the mucous cells, $13.0{\pm}0.22,\;10.2{\pm}0.05,\;and\;7.5{\pm}0.42$ in the serous cells. and $10.5{\pm}0.40,\;13.6{\pm}0.32,\;and\;15.9{\pm}0.42$ in the duct cells, while the $mean{\pm}S.D.$ of the values obtained from the 3 cell types 1, 10 and 24 hr after $[^3H]$ thymidine were $10.9{\pm}0.28,\;12.4{\pm}0.31,\;and\;10.0{\pm}0.39.$ Thus the radioactive indices obtained from the ginseng-ACTH group were generally lower than those obtained from the saline-ACTH group. It is inferred from the above results that the ginseng tends to promote the suppressive action of ACTH upon DNA synthesis of cells in the mandibular gland.