One hundred and fifteen patients with chronic hepatitis C were administered interferon (IFN) and classed into two groups: (i) complete responders (CR), HCV-RNA continuously negative 1 year after treatment; and (ii) non-responders (NR), positive 1 year after treatment. Multivariate analysis comprised eight variables: age, sex, transfusion history, alanine aminotransferase level, viral genotype, level of viremia, type of IFN, and total amount of IFN. The HCV-RNA level was correlated with complete response (P = 0.0175). Liver biopsy specimens were classified into four grades and stages according to the measure of severity and the extent of fibrosis, respectively. There was no correlation between the efficacy rate and grading. However, in staging there was a difference in the efficacy of IFN between stages 1 or 2, and stage 3 (0.05 < P < 0.1 and 0.01 < P < 0.025, respectively). Of the CR patients, 0% (0/5) were at stage 0 (no fibrosis); 27.5% (22/80) at stage 1 (mild); 42.9% (6/14) at stage 2 (moderate); and 6.3% (1/16) at stage 3 (severe fibrosis). Thus the new classification would be useful in predicting roughly the efficacy of IFN.