A review of the histopathology and demonstration of alpha-interferon with a monoclonal anti-alpha-interferon antibody reagent were carried out in 71 consecutive cases of acute and chronic hepatitis, and also in some cases of cirrhosis and HCC. The main cells expressing alpha-interferon were lymphocytes, plasma cells, fibroblasts and polymorphonuclears. There was no evidence for local alpha-interferon production near the site of virus replication in hepatitis B infection. Eleven cases of hepatitis were positive for alpha-interferon. The carrier state showed the highest positive rate in the different types of hepatitis. The positive rate in acute and chronic persistent hepatitis was lower than that in carrier state but higher than that in cirrhosis and HCC. The alpha-interferon positive cells were mainly located in the portal area and in the fibrotissue band around the necrotic and/or carcinomatous cells. These suggest that the function of the interferon system was related mainly to the pathological changes of liver tissue. Early use of interferon might be of therapeutic value to protect liver tissue from injury and to improve the interferon response of the host.