Distal esophageal pH less than 4 is frequently seen during meal ingestion in 24-hr ambulatory pH monitoring for the diagnosis of gastroesophageal reflux disease (GERD). The characteristics of this meal-related apparent reflux without diet restriction was evaluated. Data from normal volunteers (N = 21) and consecutive patients (N = 66) referred with heartburn and/or chest pain were studied with ambulatory pH monitoring. The median percent times pH < 4 in the distal esophagus were significantly greater in symptomatic patients than controls for total 24-hr, upright, and supine periods, and postprandial periods of 30, 60, 90, 120, and 150 min (P values of 0.007-0.03). However, the median percent time pH < 4 during the meal periods was the same for patients (4.4%) and for controls (6.6%) with P = 0.23. Excluding the meal periods from analysis resulted in greater separation between controls and patients with abnormal acid exposure when compared to the conventional method. Patients should maintain their usual routine without diet restriction during 24-hr ambulatory pH studies in the clinical setting. Furthermore, exclusion of meal periods can eliminate meal-time pH variabilities without affecting postprandial acid exposure and improve the diagnosis of GERD.