The pathogenesis of Sjögren's syndrome is poorly understood. Genetic and environmental factors appear to contribute to the development of this syndrome. Viral infection is one of the most likely environmental factors. The primary lesion of Sjögren's syndrome is in the exocrine glands. A majority of the infiltrating cells in the lesion are CD(4+) CD45RO(+) memory T cells. Although antigen-presentation to T cells seems to occur in the exocrine tissues, these T cells are not fully activated. On the other hand, B cells comprise approximately 20% of the infiltrating cells, and several features of this syndrome are attributed to stimulated B cells. The presence of autoantibodies, such as anti-SS-A/Ro and SS-B/La antibodies, is one of the characteristic features and is associated with severe disorders. Some antibodies appear to play a direct pathogenic role, for example, in cases of congenital heart block and sicca symptoms. Chronic inflammation with possible T cell-dependent antigen stimulation appears to induce neoplastic transformation of lymphocytes.