Previous intravenous drug abusers with chronic hepatitis C who are under substitution therapy (buprenorphine, methadone) will be treated with PegIntron and Rebetol according to the approved European labeling. The study will assess the tolerability, safety and efficacy of the treatment with PegIntron plus Rebetol in this study population. The objective of the study is to collect data on the prevalence of the hepatitis C infections in drug-substituted patients. The study will also compare the feasibility of HCV (Hepatitis C Virus) treatment in patients receiving Subutex® vs other drug substitution pharmacotherapies.