Treatment of chronic hepatitis C infection with interferon has been disappointing, with less than one third of patients achieving a sustained response and most experiencing significant side effects. For these reasons, an open-labeled prospective pilot study was conducted to test the safety and efficacy of the antiviral drug, amantadine, in patients with chronic hepatitis C infection who had previously failed therapy with interferon-alpha 2b. Twenty-two patients with chronic hepatitis C were enrolled into the study and treated with amantadine 100 mg orally twice daily for six months. Control groups included the same cohort followed off therapy for 29-36 months or during therapy with interferon. Serum alanine aminotransferase (ALT) values decreased in 64% (P = 0.01) of patients with amantadine therapy compared to intervals without therapy or to interferon therapy. Twenty-seven percent of patients treated with amantadine had normalization of ALT values and loss of HCV RNA after six months while 18% achieved a sustained response with loss of HCV RNA by PCR six months after discontinuation of amantadine. Therapy with amantadine improved both biochemical and virological markers in patients with hepatitis C who had previously not responded to treatment with interferon.