Primary Sjögren's syndrome (PSS) is an autoimmune inflammatory disorder characterized by lymphocytic infiltration of exocrine glands, B cell hyperactivity and autoantibody production. The aim of this study was to determine the presence of IL-10 and IL-13 in this disease. We studied the IL-10 and IL-13 gene expression in vivo by peripheral blood mononuclear cells and minor salivary glands from PSS patients. We found a high expression of the IL-10 gene and its product by their peripheral blood mononuclear cells (PBMC) as well as by their salivary glands. Peripheral blood B cells and monocytes were responsible for 89% of total IL-10 secretion. IL-13 gene expression was not observed in PBMNC from either PSS patients or healthy controls, and was confined to PSS salivary glands. Our results suggest that IL-10 and IL-13 contribute to the pathogenesis of PSS and might explain the B cell abnormalities and the development of lymphoma observed in this autoimmune disease.