Saponins extracted from ginseng stems and leaves (GSLS) as well as the synergistic effect between GSLS and oil emulsion were investigated for their adjuvant effects on the immune responses of mice to vaccination against foot-and-mouth disease virus (FMDV) serotype Asia 1. In experiment A, ICR mice were subcutaneously immunized twice with FMDV antigen with or without GSLS (0, 1, 5, 10 and 20 microg) at 3 week intervals. Highest FMDV-specific IgG level was observed 2 weeks after the boosting in mice immunized with FMDV antigen plus 10 microg of GSLS. In experiment B, mice were subcutaneously injected with FMDV antigen with or without GSLS (10 microg), or in oil emulsion with or without GSLS (10 microg) on days 1 and 21. Results indicated that when co-administered with a mixture of oil and GSLS, FMDV antigen induced significantly higher IgG titer and IgG1, IgG2a, IgG2b and IgG3 responses, production of IFN-gamma (Th1 cytokine) and IL-5 (Th2 cytokine) by splenocytes, as well as T and B lymphocyte proliferation in response to Con A and LPS than when FMDV antigen was used alone or mixed with either GSLS or oil. This suggests that GSLS and oil adjuvant synergistically promote both Th1 and Th2 immune responses. As protection against FMDV requires both cellular and humoral immune responses, the combined effects of GSLS and oil deserve further study in other animals such as cattle and pigs in order to induce effective immunity against FMDV infection.