Beta2-Microglobulin is normally present in low concentrations in serum and other bodily fluids. By use of a radioimmunoassay, elevated concentrations of beta2--microglobulin were found in saliva and synovial fluid from patients with Sjogren's syndrome and rheumatoid arthritis, autoimmune inflammatory diseases that attack and destroy the salivary glands and articular tissues, respectively. Elevated beta2-microglobulin concentrations decreased in the saliva of two patients who simultaneously showed a clinical response to systemic treatment. Measurement of beta2-microglobulin in inflammatory fluids may offer a simple method of quantifying local activity in autoimmune states.