The correlation between the histological features of liver biopsy specimens before interferon (IFN) treatment and the clinical effect of IFN administration on chronic hepatitis C was investigated. A study of the relation between several histological features that were graded in 60 liver biopsy specimens from chronic hepatitis C patients before IFN treatment disclosed that the grade of portal fibrosis was positively correlated with the grade of other inflammatory features, including piecemeal necrosis and portal and lobular inflammation. The degree of portal fibrosis adversely affected the rate of normalization of ALT levels in chronic hepatitis C during and after IFN treatment. We reexamined 36 liver biopsy specimens that showed a moderate degree of portal fibrosis, and found that the degree of piecemeal necrosis was inversely correlated with the extent of lymphoid follicle formation in the portal tracts. During IFN therapy, the group of chronic hepatitis C patients who showed marked piecemeal necrosis and less lymphoid follicle formation in the liver specimens had a poor response to IFN treatment, whereas another group that showed marked lymphoid follicle formation and little piecemeal necrosis in the liver specimens had a good response to IFN. These relationships gradually disappeared after the completion of IFN treatment.