Non-ulcer dyspepsia (NUD) is a common complaint in which no systematic illness or organic proximal alimentary tract disease can be identified. The pathophysiology of NUD is probably heterogeneous. Eighty-two subjects with NUD were studied in a prospective randomized placebo-controlled study to assess the efficacy of colloidal bismuth subcitrate (CBS) chewable tablets at a dose of four tablets daily for 1 month. The role of Campylobacter pylori and associated histological gastritis was evaluated. Sixty-one percent of NUD patients had C. pylori in the gastric antrum compared with 25% of age-matched controls. C. pylori was associated with acute and chronic inflammation (P less than 0.001) in the antrum. C. pylori was cleared in 59% of CBS-treated subjects compared with only 4% placebo (P less than 0.05). Both acute and chronic inflammation improved in subjects cleared of bacteria. Clearance of C. pylori and histological improvement was associated with a significant decrease in symptoms. In C. pylori negative subjects improvement in symptoms occurred in both the placebo and active treatment groups. This study would suggest that C. pylori and associated histological gastritis may play a role in non-ulcer dyspepsia.