A 24 hour esophageal pH recording was performed in 46 infants (age: 10 +/- 12 months). Two probes were placed in the proximal and distal esophageal sites respectively. A significant correlation was shown between the upper and lower part of the esophagus for the numbers of acid (pH fall below 4 for at least 15 s) and weakly acid (fall in pH of more than one unit, irrespective of whether or not the pH fell below 4) gastroesophageal reflux (GER), the reflux index and the number of acid GER longer than 5 min. The number of acid GER and the time spent at pH less than 4 at the proximal esophagus were significantly greated in group 1 (reflux index greater than 5% in the distal esophagus, n = 10), than in group 2 (reflux index less than 5% in the distal esophagus, n = 36). The proportion of distal acid and weakly acid reflux reaching the upper esophagus presented with marked variation coefficients. These findings indicate that data obtained in the distal esophagus are poorly predictive of the results in the proximal esophagus, even if infants present high reflux index at the lower esophagus. Weakly acid GER reached the upper esophagus more frequently than acid GER.