ABSTRACT—Surgically obtained liver specimens from four patients with primary biliary cirrhosis (PBC), Stages I–II, were studied immunohistochemically using a broad panel of monoclonal antibodies. At the site of bile‐duct injury (CNSDC), the inflammatory cells were recognized to be Coulter T‐11+ (directed against all T‐cells) and OKT‐8+ (directed against cytotoxic/suppressor: C/S T‐cells) cells. The MHC‐class I antigen (i.e. HLA‐A, B, C) was expressed weakly in the cytoplasm of the minority of damaged bile‐duct epithelial cells, and the MHC‐class II antigen (i.e. HLA‐DR) was not expressed. Thus, OKT‐8+ cells may play an important role in the immunologically mediated destruction of ductular epithelium in PBC. Strong MHC‐antigen expression and OKT‐8+ cell infiltration in destructive bile‐duct lesions were not simultaneously observed. In the portal lymphocyte‐rich areas, OKT‐4+ (directed against helper/inducer: H/I T‐cells) predominated over OKT‐8+ cells. B‐lymphocytes were present predominantly in the peripheral zones of the lymphoid aggregates. The distribution of helper/inducer T‐cells and B‐lymphocytes indicates that they may play a role in the induction of immunoglobulin in the lymphocyte‐rich areas. The inflammatory mononuclear cells within the granuloma observed in one patient were Coulter T‐11+, OKT‐8+ and Leu‐3