Specimens of salivary gland tissue from 21 cases of SS were analyzed by ABC immunohistochemistry technicue with a monoclonal antibody to HLA-DR. The results showed that positive immunostaining for HLA-DR were found in duct cells, acinar cells and a part of infiltrating cells respectively. The proportions of duct and acinar cells expressing HLA-DR were not increased between SS and controls. However, there are differences in their staining intensity. The HLA-DR expression on the epithelial cells in SS was most intense than in controls. Our data suggest that the HLA-DR expression of SS may be regarded as an important factor in local immune rections.