BACKGROUND: Patients with gastrointestinal reflux disease GERD perceive < 5% of acid reflux episodes, independently of GERD type. The role of minimal changes on esophageal pH (1 or 2 units) on development of symptoms is unknown. OBJECTIVE: To evaluate symptom perception and its relationship with minimal changes on esophageal pH in patients with erosive and non-erosive GERD (NERD). PATIENTS AND METHODS: We evaluated consecutive patients with symptomatic GERD. All patients had endoscopy in the previous 8 weeks. All patients underwent 24-h esophageal pH-monitoring. Abnormal pH-metry was defined as % time of pH < 4 > 4.2. Symptom index (SI) was considered positive when > or = 50. We also calculated SI at pH 5 and pH 6. Patients with GERD were classified into three groups: 1) abnormal pH and negative SI. For statistical analysis, we used the test-Student, chi 2, and ANOVA test. P < 0.05 was considered statistically significant. RESULTS: We evaluated 120 patients, 79 (66%) females and 41 (34%) males with mean age of 47.8 years (range 21-83 years). Eighty three (69%) patients had NERD and 37 (31%), erosive esophagitis (EE). Seventy two patients (87%) with NERD and 36 (97%) with erosive GERD developed symptoms during the study. NERD patients had mean of 69 reflux episodes compared with 184 of patients with EE. Perception of reflux symptoms was significantly higher in the group with EE (3.4 vs. 1.02 p < 0.0001). Among patients with NERD, 33% had abnormal pH-metry and 67%, a normal test. Of these patients, nine (16%) had normal pH test and positive SI, and 47 (83%) normal pH test and negative SI. There was no difference in symptom perception among the three groups. Patients with NERD and abnormal pH had similar SI patients with EE; 4% of patients with normal pH and negative SI at pH 4 had positive SI when calculated at pH 5, and 68% when SI was calculated at pH 6. CONCLUSIONS: The majority of acid reflux episodes are not perceived and this phenomenon is independent of erosive or non-erosive GERD. Patients with erosive esophagitis had significantly higher esophageal acid exposure than patients with NERD. Minimal changes in esophageal pH (1 or 2 pH units) increases SI in patients with GERD, especially in those with normal esophageal acid exposure.