Sjogren's syndrome is a chronic systemic disease that primarily affects the salivary and lacrimal glands and is characterized by lymphocytic tissue infiltration and auto-antibody production. The pathogenesis of Sjogren's syndrome is unknown. We hypothesize that reduced somatostatin activity is an important factor in promoting immune dysregulation in patients affected by Sjogren's syndrome. Somatostatin is a multifunctional peptide with potent immunomodulatory properties whose effects are reduced lymphocytic activity, reduced gastrointestinal secretions, activation of the hypothalamic-pituitary axis, anti-inflammatory, etc. As several findings in Sjogren's syndrome are opposite to those produced by somatostatin, it is logical to consider that the activity of this peptide is low in patients affected by this disease. The purpose of this study is to determine whether basal and stimulated plasma levels of somatostatin and its effects on the immune and endocrine systems differ between 16 patients affected by primary Sjogren's syndrome and 16 healthy control subjects.