Results of an experiment on the behavior of rats and mice in order to explore the possible pharmacological actions of Panax ginseng upon the central nervous system can be summarized as follows: 1. Spontaneous motor activity. In the case of mice, those groups who were administered 2.5 mg and 5.0mg of ginseng saponin per kilogram of body weight were observed to have increased their activity compared with the control group, while the 50.0 mg and 100.0 mg per kilogram body weight groups demonstrated lower levels of activity, with the peak of activity appearing at 30 minutes after administration of drugs. In the case of rats, those groups of animals who were given injections in the dosage of 2.5 mg, 5.0 mg and 50.0 mg per kilogram body weight demonstrated higher activity than the control group, while the 100.0 mg per kilogram group appeared to have decreased in their activity, with the peak action appearing 30 minutes after the administration of ginseng saponin. The 50.0 mg per kilogram group demonstrated no significant differential. 2. General behavior analysis. In the case of mice, decrease in sleeping component of behavior and increase in the walking and roaring components, compared those with the control group, turned out to be a common phenomenon among the groups who were administered 2.5 mg, 5.0 mg and 50.0 mg of ginseng saponin per kilogram body weight, with the 5.0 mg per kilogram group standing out of all the other groups in terms of their reactions. In the case of rats, ginseng saponin appeared to reduce sleeping component with 2.5 mg, 5.0 mg and 50.0 mg per kilogram body weight groups, while increased the walking and rearing components. It was observed that administratoin of ginseng saponin in a dose of 2.5 mg per kilogram appeared to markedly increase the lying and grooming components of animal behavior. 3. Open-field exploratory behavior. Adminstration of ginseng saponin to mice in doses of 5.0 mg, 50.0 mg and 100.0 mg per kilogram body weight decreased activity, but increased their exploratory behavior. In the case of rats, however, administration of ginseng saponin in the doses of 2.5 mg and 5.0 mg per kilogram body weight markedly increased their activities, while decreased activities with the 50.0 mg per kilogram and 100.0 mg per kilogram groups. The exploratory behavior of rats appeared to have decreased, while grooming increased ramarkably. 4. The above findings from a series of experiment appear to suggest a stimulating effect on the central nervous system when ginseng saponin is administered in small doses, but that larger doses might result in an inhibitory effect, though differential results can be anticipated with modification of experimental conditions.