According to the localization of hepatitis B virus (HBV) core antigen (HBcAg), detected by the avidin-biotin complex method, infected hepatocytes were classified into three types, i.e. those having nuclear (type I), nuclear and cytoplasmic (type II) or only cytoplasmic (type III) antigen. HBcAg-positive hepatocytes of all specimens (three) from non-specific reactive hepatitis and of most (five of seven) from chronic persistent hepatitis (CPH) patients were only type I; the other two CPH samples and all (seven) chronic active hepatitis samples were composed of a mixture of types I, II and III. Linear correlations between the frequency of type I, as well as that of of all types (I, II and III) of the HBcAg-positive hepatocytes, and the amount of HBV DNA in serum were found. The relative HBV production of HBcAg-positive hepatocytes (serum HBV DNA amount/frequency of HBcAg-positive cells) was 0.11 in type I and 0.07 in all hepatocytes including types I, II and III. HBV core particles and complete HBV particles were found in type I hepatocytes. On the other hand, these particles were not found in a predominantly type III liver specimen. These results suggest that type I hepatocytes are more involved in the propagation of HBV than types II and III.