The frequency of occurrence of hepatitis B antigen (HBAg) and certain tissue autoantibodies [antinuclear antibody (ANA), smooth muscle antibody (SMA) and mitochondrial antibody (MIA)] were studied with the microtiter complement fixation and immunofluorescence techniques respectively in a group of patients suffering from chronic liver diseases. These were chronic hepatitis (30), cirrhosis of the liver (66) and hepatocellular carcinoma, mostly with underlying cirrhosis (100). A group of closely matched hospital in-patients served as controls. HBAg was found in high frequency in the patients with liver disease (60% in chronic hepatitis, 36.4% in cirrhosis and 49% in hepatocellular carcinoma) whereas tissue auto-antibodies were found in lower frequencies (16.7%, 10.6% and 13% in the three groups respectively). However, in both the frequency was significantly higher than that in the controls (9.2% for HBAg and 0.8% for auto-antibodies). There was a negative correlation between HBAg and tissue auto-antibodies in the group of patients with liver disease when taken as a whole (x2=14.3, P less than 0.001). These results suggest a possible aetiological role played by hepatitis virus B in hepatocellular carcinoma through chronic hepatitis and cirrhosis in Hong Kong while the mutual exclusion between HBAg and auto-antibodies supports the hypothesis of heterogeneity in the aetiology of chronic liver diseases. The patients with auto-antibodies may belong to the auto-immune category but no definate conclusion can be reached until the role played by hepatitis virus A in chronic liver diseases is clarified when more reliable techniques for its identification are available.