Treatment of hepatitis C with interferon and ribavirin has a virological effect. Viral hepatitis C prognosis is related to the presence of a fibrosis and to the risk of developing cirrhosis or hepatic cancer. In vitro studies of prazosin suggest an effect against hepatic fibrosis, but the clinical effect of prazosin on the hepatic fibrosis induced by hepatitis C infection is unknown. The purpose of this multicentric national study is to compare the effects among the hepatic fibrosis of peg-interferon alpha 2b and ribavirin with prazosin or not (placebo). 112 patients with a viral hepatitis C, genotype 1 or 4, and severe fibrosis, will be randomly assigned to one of two treatment groups: peg-interferon alpha 2b and ribavirin, with prazosin or with placebo. Peg-interferon alpha 2b will be administered once a week (1.5 micro g per kg) during 48 weeks, ribavirin 1,000 to 1,200 mg per day (according to weight) during 48 weeks, prazosin/placebo 5 mg (2 pills) per day during 96 weeks. Evaluation will be done at 96 weeks. The primary end-point is the proportion of patients presenting a decrease of fibrosis. Secondary end-points are other criteria of histological response, virological response, biochemical response.