Twenty-two full-term infants, nine asymptomatic and 13 symptomatic for chronic digestive problems, had long-term (mean = 21 h) esophageal pH monitoring. All children were observed in strictly standardized conditions including meals and body position. Symptomatic infants presented significantly more esophageal refluxes, spent a greater percentage of time with a pH below 4, had a longer reflux duration (longer clearing time) and presented more refluxes lasting more than 5 min. We performed a determination of the circadian variations of parameters associated with esophageal reflux. Asymptomatic and symptomatic infants presented significant circadian variations of the percentage of time below pH 4 and of the longest duration of reflux. However, symptomatic infants had significantly higher mean values and increased amplitudes of circadian rhythms. Moderate phase lag existed for certain variables between symptomatic and asymptomatic infants. These findings can be helpful when interpreting the results of long-term esophageal pH monitoring.