We randomly assigned 159 patients with non-ulcer dyspepsia, defined as chronic or recurrent epigastric pain without concomitant symptoms of the irritable bowel syndrome and with no evidence of organic disease, to treatment for three weeks with an antacid suspension one and three hours after meals, 400 mg of cimetidine twice a day, or placebo, according to a double-blind, double-dummy model. The intensity and duration of epigastric pain were recorded by the patients four times daily during a one-week period without therapy and during the three weeks of treatment. The mean reduction in pain intensity after three weeks in the placebo group was 25 percent. Neither antacid nor cimetidine treatment resulted in more than a 4 percent better effect. The reduction of pain was statistically significant (P less than 0.01) in all three groups. The time course of the pain scores in the groups receiving active drugs followed closely those in the placebo group, and there were no significant differences between the groups at any stage of the treatment. We conclude that the neutralization or suppression of gastric acid is of no clinical value in patients with this syndrome.