Ginseng radix (Panax ginseng C.A. Meyer) is a popular herbal medicine used as a major ingredient in tonic recipes in eastern Asian countries. In our study, male BALB/c mice were treated orally with various doses of ginseng root extract for 5 consecutive days. The extract reduced the serum level of IgG but elevated the level of IgA. Under in vitro condition, the lipopolysaccharide-stimulated spleen cells from the ginseng-treated mice also showed a significant decrease in IgG production but an increase in IgA production. The serum level and production of IgM was unaffected. The interleukin-2, interferon-gamma (Th1-type cytokines), and interleukin-10 (Tr1-type cytokine) production by Con A-stimulated spleen cells from the ginseng-treated mice showed an upregulation relative to the control group. However, the production of interleukin-4 (Th2-type cytokine) showed no significant change. The activity of natural killer cells was increased in the ginseng group, but the percentages of T-lymphocytes (CD3(+)) and CD4(+)8(-), CD4(-)8(+) subset were reduced. Thus, short-term oral administration of ginseng extract appears to enhance Th1-type cytokine production.