We performed two courses of interferon-beta (IFN-beta) to a child with chronic hepatitis C. A complete response was not obtained by the first interferon treatment, however, the results of the second treatment differed from those of the first. Hepatitis C virus (HCV)-RNA remained negative and both aspartate aminotransferase and alanine aminotransferase levels remained normal after completion of the second course. From these results we estimated that HCV-RNA levels before IFN therapy could be significantly associated with the efficacy of this treatment. The serum level of HCV-RNA was 10(6) copies/50 microL before the first treatment, but was 10(3) copies/50 microL before the second course. We conclude that IFN therapy to children with hepatitis C should always be directed at providing a cure. Even if the clinical effects of the first course are minimal decreasing quantities of HCV-RNA still offer hope for cure by subsequent readministration.