Patients with dyspepsia of unknown origin were randomly allocated to a controlled double-blind study to examine the symptomatic effect of cimetidine and antacid especially on the relief of pain, nausea, and bloating. Two hundred and twenty-two patients with no previous history of peptic ulcer disease and no evidence of other organic causes of dyspepsia were treated for 6 weeks with placebo, cimetidine, or antacid. The results showed that cimetidine was superior to both placebo and antacid in relieving pain and nausea but not bloating. Certain background factors, such as epigastric pain and symptoms relieved by solid food, had a significant positive influence on the outcome of treatment. When the impact of background factors was taken into account, cimetidine was found to be more effective than both placebo and antacid also with regard to the number of patients who improved in general well-being.