Gastroesophageal reflux was investigated in 80 patients with duodenal ulcer by analysis of symptomatology and the acid reflux test. Resting gastroesophageal sphincter pressure (GESP) and postvagotomy reduction in basal and pentagastrin stimulated gastric acid secretion were also studied. Reflux symptoms were present in 40% of the patients, and this incidence was significantly reduced two months after vagotomy. In patients studied late after operation reflux symptoms were still less frequent than before operation, but not significant. After vagotomy, no significant changes in the fasting GESP or in gastroesophageal reflux as determined by the pH glass electrode were demonstrated. Thus, the decrease in reflux symptoms may be explained by the significant reduction in gastric acid secretion. Denervation of the cardia and the lower esophagus does not influence GESP or gastroesophageal reflux.