The root of Panax ginseng C.A. MEYER has been reported to have an anti-stress action. Therefore, the effects of ginseng components on functions of adrenal medulla, which is one of the most important organs responsive to stress, were investigated in vitro. First, the components of ginseng were mainly divided into two fractions, that is, the saponin-rich and non-saponin fractions. The saponin-rich fraction greatly reduced the secretion of catecholamines from bovine adrenal chromaffin cells stimulated by acetylcholine (ACh), whereas the non-saponin fraction did not affect it at all. The protopanaxatriol-type saponins inhibited the ACh-evoked secretion much more strongly than the protopanaxadiol-type. On the other hand, the oleanane-type saponin, ginsenoside-Ro, had no such effect. Recent reports have demonstrated that the saponins in ginseng are metabolized and absorbed in digestive tracts following oral administration of ginseng. All of the saponin metabolites greatly reduced the ACh-evoked secretion. M4 was the most effective inhibitor among the metabolites. M4 blocked ACh-induced Na(+) influx and ion inward current into the chromaffin cells and into the Xenopus oocytes expressing human alpha3beta4 nicotinic ACh receptors, respectively, suggesting that the saponin metabolites modulate nicotinic ACh receptors followed by the reduction of catecholamine secretion. It is highly possible that these effects of ginsenosides and their metabolites are associated with the anti-stress action of ginseng.