To examine whether Sho-saiko-to (kampo medicine) could modulate the immune response of immunocompetent cells to hepatitis B virus (HBV)-associated antigens, we investigated in vitro interferon gamma (IFN-gamma) and antibody (antibody to HB core and e antigens; anti-HBc and anti-HBe) production by peripheral blood mononuclear cells (PBMC) from eight patients with chronic active hepatitis (CAH) (four with HBeAg and four with anti-HBe) in the presence of recombinant HBcAg and purified HBeAg. IFN-gamma and antibody production were measured using ELISA and RIA, respectively. PBMC from both HBeAg and anti-HBe positive patients generated significantly increased IFN-gamma and antibody (anti-HBc and anti-HBe) production in the culture containing Sho-saiko-to (TJ-9) in a dose-dependent manner in comparison with those of medium alone culture. Similarly, when various concentrations of TJ-9 were added to the HBV antigen-stimulated cultures, TJ-9 was found to enhance both IFN-gamma and antibody production dose-dependently. These results indicate that TJ-9 is able to modulate both cellular and humoral immune responses specific for HBV-associated antigens. These findings also may account for, at least in part, the efficacy of TJ-9 treatment for type B chronic hepatitis.