The efficacy was evaluated of a herbal medicine (Mao-to) on psychiatric complications caused by interferon (IFN), and the relationship between depression and microcirculation examined. Twelve patients with chronic hepatitis C and a past history of IFN-induced depression were enrolled in this study. Their mental state was evaluated by the self-rating depression scale ≥40, or M-R of the Cornell medical index (CMI) ≥10. Each patient received a daily dose of 6 million units of IFN-beta for 8 weeks, and Mao-to was given orally four times a day during the IFN-beta course. All patients in this study completed a full course of IFN. Mean CMI scores (M-R) had significantly decreased at the end of the treatment. Mean erythrocyte aggregation and erythrocyte deformability had also significantly decreased at the end of treatment.