Recent studies have suggested that the induction of HLA—DR antigens on epithelial cells plays an important role in the pathogenesis of autoimmune endocrine‐exocrine disorders. We found that salivary gland epithelial cells (i.e., acinar and ductal cells) in salivary gland biopsy specimens from patients with primary Sjögren's syndrome (keratoconjunctivitis sicca) expressed high levels of HLA—DR antigen, which were detected by staining frozen tissue sections with monoclonal antibodies and immunoperoxidase technique. In contrast, salivary gland epithelial cells from normal subjects did not express this antigen. Lymphocytes eluted from the salivary gland biopsy specimens of patients who had Sjögren's syndrome produced a soluble factor that stimulated HLA—DR synthesis by a salivary gland‐derived cell line (Sal‐1). These tissue culture supernatants contained γ‐interferon, and their ability to induce HLA—DR synthesis was blocked by monoclonal anti‐γ‐interferon antibody. These results demonstrate the presence of HLA—DR antigen on salivary gland epithelial cells and suggest that local production of γ‐interferon plays a role in this induction.