Peripheral blood samples were collected from normal subjects and chronic viral hepatitis patients, and the in vitro capability of the peripheral blood mononuclear cells to produce various cytokine (interleukin-1 beta, interleukin-6, interferon-gamma, and granulocyte-macrophage colony-stimulating factor) were analyzed by adding pokeweed mitogen. We then investigated the effects of a herbal medicine "Sho-saiko-to" on the levels of cytokine production. The production levels of the 4 cytokines were significantly lower in the peripheral blood mononuclear cells of the patients (Patient Group) than in those of normal subjects (Control Group). The addition of Sho-saiko-to to the Patient Group resulted in improved productions of those cytokines, as well as an remarkable improvement of interleukin-1 beta production. The results demonstrated that Sho-saiko-to acts to improve such immunological abnormalities as decreased cytokine productions. Administration of Sho-saiko-to to chronic viral hepatitis patients is also expected to have immunological benefits.