Since the 1997 National Institutes of Health Consensus Development Conference on management of hepatitis C there have been several important advances that significantly impact its therapy; notably the availability of sensitive, specific, and standardized assays for identifying hepatitis C virus (HCV) RNA in the serum, the addition of ribavirin to alpha interferon, the pegylation of alpha interferon, and the demonstration that sustained virological response (SVR) is the optimal surrogate endpoint of treatment. Using pegylated interferon and ribavirin, virological response with relapse and nonresponse are less common, but remain poorly understood. Current studies are evaluating nonvirological endpoints of treatment, namely biochemical response and histological response. To date, definitive treatment trials have primarily been conducted in adult patients with elevated aminotransferase levels, clinically compensated chronic liver disease, and no other significant medical disorder. Limited data are available from studies of other patient populations, and the safety of interferon-based treatment has not yet been established in several patient groups. Future research is needed to elucidate the mechanisms of viral response and clearance, to develop effective therapies for interferon nonresponse or intolerance, to define the role of complementary and alternative medicine and other nonspecific therapies, and to develop strategies for the optimal management and treatment of special patient populations who probably represent the majority of persons with chronic hepatitis C in the United States.