A continuous 24-h esophageal pH monitoring was performed in 283 asymptomatic infants between 5 days and 15 months old. Several parameters (reflux index, duration of the longest reflux episode, number of reflux episodes in 24 h, number of reflux episodes greater than 5 min in 24 h) were studied in different groups of infants according to their age: 5-15 days old, 24-37 days old, 3.5-4.5 months old, 5.5-6.5 months old, 7.5-8.5 months old, 14-16 months old. For all parameters we obtained statistically significant different results in infants younger and older than 4 months. The 24-h esophageal pH monitoring is an investigation technique in physiological circumstances in order to establish normal ranges for gastroesophageal reflux in asymptomatic infants.