We investigated the efficacy of retreatment with interferon in patients with chronic hepatitis C who were non responders to the initial interferon treatment. The results were as follows: 1) The effective rate was very low and 2 of the 16 responded to the 2nd treatment. 2) Serum HCV-RNA levels before retreatment with interferon were compared among the 4 responders and the 13 non responders to interferon and it was significantly lower in the 4 responders. 3) HCV-genotypes may be useful to predict the efficacy of interferon readministration.