The purpose of this study was to evaluate possible differences in basal gastric acid secretion with regard to severity of gastroesophageal reflux disease. Basal acid output was determined by nasogastric suction in 228 patients with gastroesophageal reflux disease who received upper gastrointestinal endoscopy and were diagnosed with either pyrosis alone (N = 98), erosive esophagitis with or without pyrosis (N = 87), or Barrett's esophagus (N = 43). Mean basal acid output for the 228 patients with gastroesophageal reflux disease was 6.5 +/- 5.6 meq/hr, which was significantly different from 65 normal subjects with a mean basal acid output of 3.0 +/- 2.7 meq/hr (P < 0.0001). Compared to normal subjects, mean basal acid outputs significantly differed for patients with pyrosis (P < 0.05), esophagitis (P < 0.01), and Barrett's esophagus (P < 0.01). There was also a significant difference in mean basal acid output between the patients with pyrosis and Barrett's esophagus (P < 0.01). Nineteen of the 98 patients with pyrosis (19%), 24 of the 87 patients with esophagitis (28%), and 15 of the 43 patients with Barrett's esophagus (35%) had gastric acid hypersecretion (basal acid output greater than 10.0 meq/hr). One hundred forty-six patients with gastroesophageal reflux disease were treated with ranitidine in doses that resulted in complete healing of esophagitis and disappearance of pyrosis. Ninety-three patients responded to ranitidine 300 mg/day; however, 53 patients required increased dose of ranitidine (mean 1205 mg/day, range 600-3000 mg/day).(ABSTRACT TRUNCATED AT 250 WORDS)