A prospective case controlled study was conducted to evaluate the role of fluoride as a possible aetiological factor for non-ulcer dyspepsia (NUD). Twenty patients with NUD and 10 age and sex matched healthy controls were subjected to clinical evaluation, upper gastrointestinal endoscopy and biopsies from the gastric antrum and duodenum. The antral and duodenal mucosa was subjected to a rapid urease test for Helicobacter pylori and histological and electron microscopic examinations. Fluoride levels in the drinking water, serum and urine were estimated using a ION 85 ion-analyser. These levels were significantly higher in patients with NUD than in controls (P less than 0.05). Histological abnormalities in the antral and duodenal mucosa were seen in 14 patients (70%) with NUD and 1 control subject (10%) (P less than 0.05). Electron microscopic abnormalities in the mucosal cells were seen in all patients with NUD but in none of the controls (P less than 0.01). The fluoride levels in serum and urine correlated with the symptoms, histological and electron microscopic abnormalities (P less than 0.05). It was concluded that chronic exposure to fluoride may result in NUD and should be considered in patients where other known cause of dyspepsia have been excluded.