Ribavirin is a synthetic nucleoside analogue that is active in vitro against some RNA and DNA viruses. The mechanism by which ribavirin in combination with peginterferon alfa-2b or interferon alfa-2b acts on hepatitis C virus is unknown. Ribavirin monotherapy for chronic hepatitis C does not result in viral elimination (hepatitis C RNA virus) or improvement in liver histology after 6-12 months of therapy and during a 6-month follow-up period. However, the combination of ribavirin with peginterferon alfa-2b or interferon alfa-2b in clinical trials has resulted in an increased response rate compared with peginterferon alfa-2b or interferon alfa-2b monotherapy.