The present study was designed to evaluate the adjuvant activities of estrogen and ginsenosides Rb1 and Rg1, saponins of Ren Shen (Ginseng). Seventy-two mice were randomly divided into 9 groups of 8 animals each. Mice were subcutaneously injected on days 1 and 21 with saline alone (Group 1), saline with 10 μg ovalbumin (OVA) (Groups 2 and 3), saline with 10 μg OVA and 30 μg of 17β-estradiol benzoate (E2) (Groups 4 and 5), saline with 10 μg OVA and 50 μg ginsenoside Rb1 (Groups 6 and 7) or saline with 10 μg OVA and 50 μg ginsenoside Rg1 (Groups 8 and 9). Animals in Groups 3, 5, 7 and 9 were injected subcutaneously with 200 μg of ICI 182780, an anti-estrogenic compound, for 3 days prior to receiving their respective study treatment. Blood samples were collected 2 weeks after the day 1 and day 21 injections for measurement of serum OVA-specific IgG and IgG subclasses. Splenocytes were harvested at 2 weeks after the day 21 injections for determination of lymphocyte proliferation and cytokines mRNA expression. Results indicated that injection of OVA together with estradiol, ginsenoside Rb1 or ginsenoside Rg1 significantly enhanced OVA-specific IgG responses, lymphocyte proliferation and cytokines mRNA expression and the enhancement could be blocked by pre-injection of an estrogen receptor antagonist ICI 182780, indicating that estrogen, ginsenoside Rb1 and ginsenoside Rg1 may exhibit the adjuvant activities through estrogen receptors.