In patients with chronic hepatitis C, the main predictors, before treatment, of sustained response to interferon therapy are serum hepatitis C virus (HCV) RNA level and HCV genotype. During treatment, early response with normalization of serum alanine aminotransferase (ALT) and negative tests for serum HCV RNA are predictive of a sustained response. In the absence of early response observed within the first three months of therapy, the chance of sustained response is very low and interruption of interferon therapy may be considered.