Sjögren's syndrome is an autoimmune disease characterized by lymphocytic infiltration and destruction of salivary and lacrimal glands. This condition may occur as a primary condition or may be associated with other autoimmune disorders such as rheumatoid arthritis or systemic lupus. Because the environmental factors that initiate SS are unknown, we have investigated the potential role of EBV, CMV, and other viruses. We observed that epithelial cells in salivary gland biopsies of patients with SS contained antigens reactive with monoclonal antibodies against EBV-associated antigens. These antigens were not found in other tissues of patients with SS and were not detectable in salivary gland biopsies from normal persons and patients with other autoimmune diseases lacking SS. The molecular weight of the antigens present in the SS salivary gland extracts was similar to that expressed in cells containing reactivated EBV. Also, the content of EBV DNA in the saliva of patients with SS was significantly greater than in age-, sex-matched controls or persons with other autoimmune disorders. These studies provide one of the first examples where a specific viral agent may be implicated in perpetuating a chronic autoimmune disease. These results also may provide insight into other autoimmune diseases where the target organ is less accessible to biopsy.