Seven women and 3 men infected with hepatitis C virus, all of whom had failed to respond to therapy with either IFN-alpha or IFN and ribavirin, were treated with 200 mg/day of amantadine hydrochloride for 12 months. We found a significant decrease of serum ALT activity without any decrease in virus load. These results suggest that amantadine hydrochloride should not be used as monotherapy for patients who do not respond to treatment with IFN-alpha and/or ribavirin.