The first-ever controlled study of a therapeutic modality for xerostomia is reported. A recently described formulation for saliva substitute (SS) has been tested against a glycerine mouthwash as a control saliva substitute (placebo) in a double-blind clinical trial in 108 patients with varying grades of xerostomia of Sjögren's syndrome. The results indicate that SS offered significant relief of nocturnal oral discomfort (p less than 0.02) and more patients reported "excellent" improvement (p less than 0.01) on a five-point graded response. In all other respects, the SS was not significantly better than the placebo. Significant adverse effects were not reported. It is suggested that any such current and future therapeutic modalities for Sjögren's syndrome be subjected to similar critical appraisal of their worth.