The effectiveness of cimetidine for symptomatic relief in patients with chronic gastroesophageal reflux was studied in a multicenter, double blind clinical trial. Patients were entered into the study for a total of 8 weeks, receiving either cimetidine, 300 mg four times daily, or identical placebo tablets. Throughout the trial, frequent assessments were made of symptom severity and frequency, combined with careful measurement of antacid use. Esophagoscopy, esophageal acid sensitivity, and lower esophageal pressures were performed before and at the completion of the treatment period. Significant (P less than 0.05) decreases in symptom frequency and severity were noted throughout the study in the cimetidine-treated patients, as compared with the placebo group. This subjective improvement was corroborated by a concomitant decrease in antacid use, which was significantly (P less than 0.05) reduced in the cimetidine-treated group. In addition, significant improvement in esophageal acid sensitivity resulted from cimetidine therapy. No objective improvement in esophageal endoscopic appearance or sphincter pressures was noted. The results of this double blind trial indicate that cimetidine is more effective than the placebo for the relief of symptoms of gastroesophageal reflux.