Little is known about the distribution of IgG-bearing cell subpopulations in normal liver and their possible changes in disease conditions. We developed an immunohistochemical method that proved suitable and accurate for the identification and characterization of IgG-bearing cells and their subpopulations in liver specimens. The method uses specific monoclonal antibodies on serial mirror liver sections. We applied this method to four normal liver tissue specimens and 25 liver biopsy samples of chronic hepatitis of viral etiology. Only rare IgG-bearing cells could be observed in the portal tracts of normal liver specimens. In contrast, a dense infiltrate of such cells was seen in liver specimens from patients with chronic viral hepatitis. The density of IgG-bearing cells in such patients ranged from 6 to 20 cells x 10(-4) micron2 in the different specimens (mean = 11 x 10(-4) micron2). The increase in IgG-bearing cells did not appear to be related to the histological diagnosis, to the degree of histological inflammatory activity or to the type of viral infection. The major population of IgG-bearing cells consisted of IgG1-positive cells (68%); IgG2- (17%), IgG3- (8%) and IgG4 (7%)-bearing cells represented only minor fractions. The increased prevalence of IgG1-bearing cells observed in chronic hepatitis but not in normal liver specimens suggests that these findings may reflect an activation of antibody production directed toward viral antigens or antigenic structures of self. The identification of the antigenic specificities of the antibodies produced by IgG-bearing cells might provide important clues in understanding the pathogenesis of chronic viral hepatitis.