With introduction of the Bilitec 2000 device, intraluminal bile monitoring has become a standard technique for evaluation of patients with gastroesophageal reflux disease and symptoms of bile reflux. A specific "white diet" excluding colored food is necessary to provide correct measurements. The influence of this specific diet on simultaneous esophageal pH monitoring is unknown. Forty patients with reflux symptoms were studied prospectively. Meal times and supine and erect phases of measurement were recorded in a standardized fashion using a patient protocol. Esophageal 24-hour pH monitoring with administration of a "colorless" diet (water, milk, potatoes, fish, chicken) was started on day 1, followed by esophageal 24-hour pH-metry with intake of a normal diet on day 2. Data from the two successive pH measurements were compared. The prevalence of a pathologic esophageal pH-metry was significantly higher during intake of a normal diet compared with a colorless diet (P=0.025). During total and upright phases, administration of a white diet led to significant reduction in the percentage of time with a pH less than 4 (P </= 0.01), the total number of reflux episodes (P </= 0.001), and the DeMeester's score (P=0.01). This difference was exclusively found in patients with a normal pH-metry (group 1, n=13) and pathologic upright reflux (group 2, n=12). No change in reflux pattern was found in patients with isolated supine reflux (group 3, n=7) and combined upright and supine reflux (group 4, n=8). In patients with a pathologic upright reflux pattern, administration of a white diet results in a significant modification of esophageal pH-metry. Data derived from simultaneous esophageal pH and bile monitoring should be interpreted with care.