We have carried out a double blind placebo controlled trial to assess the effects of treatment with colloidal bismuth subcitrate in Helicobacter pylori associated non-ulcer dyspepsia. Eighty patients with dyspepsia, normal upper gastrointestinal appearances at endoscopy and H pylori associated active chronic gastritis on histology of gastric antral biopsies were included in the trial. The patients were randomised to receive colloidal bismuth subcitrate 240mg twice daily for four weeks or matching placebo and were reassessed four weeks after completing treatment. Twenty-six patients (67%) receiving colloidal bismuth subcitrate had normal histology or improved inflammation compared with five (13%) receiving placebo (p less than 0.001), and symptoms were absent or improved in 32 (82%) and two (5%) respectively (p less than 0.001). Serum IgG level was a marker of infection, and fell with successful treatment. Colloidal bismuth subcitrate is effective treatment for H pylori associated non-ulcer dyspepsia with improved gastric antral histological appearances and has a beneficial effect on symptoms.