2,346 liver samples from 17 cities of China for intrahepatic hepatitis D antigen (HDAg) were studied by direct enzyme-labelled technique. HDAg was detected in 167 out of 1,764 samples of HBsAg positive individuals making a detection rate of 9.47%. Hepatitis D virus (HDV) infection existed in all the examined districts with no significant difference in the HDAg detection rate. It was found that the intrahepatic HDAg detection rate was related to the pathologic type of the liver disease. The HDAg detection rate in chronic liver diseases and severe hepatitis was higher than in other liver diseases. It suggests that HDV infection is associated with the progression and chronicity of the liver disease. Studies on the relationship between HDV infection and HBV replication showed that HBV replication might be suppressed by HDV infection. Both HDV and HBV, however, could replicate in the same hepatocyte simultaneously.