Hepatic histological features described in hepatitis C virus (HCV) infection include bile duct damage, lymphoid follicles and/or aggregates in portal tracts, large- and small-droplet fat, Mallory body-like material in hepatocytes, liver cell dysplasia and multinucleation, and activation of sinusoidal inflammatory cells. We have examined the frequency of these lesions in 189 liver biopsy specimens, to distinguish HCV from hepatitis B infection. We have analyzed a set of three features of tures more likely to be seen in HCV than in HBV infection: lymphoid follicles and/or aggregates (68%/20%), bile duct damage (44%/22%) and large-droplet fat (77%/64%). A fourth lesion, Mallory body-like material, was seen more frequently in HCV than HBV (25%/5%). These four histological lesions are useful pathological parameters in the diagnosis of liver disease caused by HCV.