Objective - To investigate eicosanoid concentrations in the saliva of patients with primary Sjögren's syndrome (SS). Methods - Whole mixed saliva of 36 subjects was assayed for eicosanoid concentrations using a radioimmunoassay. Patients with primary SS having positive lip biopsy served as the study group; their results were compared with data from patients with dry mouth and negative lip biopsy (dry mouth group), and with a group of normal healthy controls. Results - Concentrations of thromboxane B2 were significantly (p < 0·01) increased in 18 patients with primary SS compared with 10 patients with dry mouth and eight healthy normal controls (1·95 (SD 0·51) ng/ ml saliva compared with 0·52 (0·1) ng/ml and 0.3 (0.1) ng/ml, respectively). Similarly, prostaglandin E2 concentrations were also significantly increased (p < 0·01) in 11 patients with primary SS compared with five patients with dry mouth and eight normal controls (3·75 (0·82) ng/ml saliva compared with 0·32 (0·1) ng/ml and 0·41 (0·1) ng/ml, respectively). Conclusion - Salivary concentrations of eicosanoids are significantly increased in patients with primary SS, and this may prove helpful in the diagnosis of this disease.