This study describes the distribution of the major histocompatibility class II antigens HLA-DR, HLA-DP, and HLA-DQ in liver tissue from eight patients with primary sclerosing cholangitis, by means of the immunoperoxidase technique on cut cryostat sections. HLA-DR was expressed on the bile duct epithelium and vascular endothelium from all patients. HLA-DP showed an expression much like HLA-DR on the bile duct epithelium, but the vascular endothelium mostly did not stain for HLA-DP. HLA-DQ was generally more weakly expressed, and only three of the patients expressed HLA-DQ on the bile ducts. None of the hepatocytes expressed any of the MHC class II antigens.