We have examined the possibility that a component of Panax ginseng, ginsenoside-Rg1 (G-Rg1), acts by binding to the glucocorticoid receptor (GR). G-Rg1 competed for [3H]dexamethasone (Dex) binding to GR with a specific affinity of 1-10 microM and activated a glucocorticoid responsive element-containing luciferase reporter gene. The dose-dependence patterns of G-Rg1 and Dex for these two effects were nearly identical, although two to three orders of magnitude higher concentration of G-Rg1 than that of Dex was required for the same magnitude of response. At the cellular level, the growth of FT02B cells was suppressed by G-Rg1 as well as by Dex, each of whose effects were abolished by RU486. These results demonstrate that G-Rg1 is a functional ligand of GR.