“Sho-saiko-to” (TJ-9) consists of 7 herbal components. In Japan, it is widely prescribed to patients with chronic viral liver disease. TJ-9 is known to suppress liver cancer development and possess macrobiotic effects, but its mode of action is not fully understood. This study investigated the following: (1) cytokine production levels, mainly interleukin (IL)-10, in peripheral blood mononuclear cells of chronic active hepatitis B and C patients, and healthy volunteers; (2) effects of TJ-9 on these productions; and (3) effects of each of its herb components on cytokine production in cell fractions. Results showed that without stimulants, IL-10 production in mononuclear cells of hepatitis B and C patients was significantly lower than that of healthy subjects (P < .01). IL-10 production induced by either phytohemagglutinin (PHA) or pokeweed mitogen (PWM) in mononuclear cells of hepatitis C patients were significantly lower than in patients with hepatitis B (P < .01) and healthy subjects (P < .05). IL-10 production induced by anti-CD3 or lipopolysaccharide (LPS) was significantly lower than in healthy subjects (P < .05). The addition of TJ-9 to the cultures strongly induced IL-10, and this induction was mainly attributable to the effects of 2 components (scutellaria root and glycyrrhiza root) on the monocyte/macrophage fraction. The production of IL-4 and IL-5 in cultures with concanavalin A (conA) was significantly higher in patients with hepatitis C than in the healthy subjects (P < .01; P < .05), but the addition of TJ-9 suppressed these increases by 25% to 33% (P < .01). Therefore, TJ-9 could adjust the decreased IL-10 production and the increased IL-4 and IL-5 production of mononuclear cells from patients with hepatitis C. Moderate regulation of the cytokine production system in patients with hepatitis C by using TJ-9 may be useful in the prevention of disease progression.