Using prolonged esophageal pH monitoring, we examined 42 infants referred for gastroesophageal reflux (GER) over a 16-month interval. Eighteen of these infants were also examined with intragastric pH monitoring following a standard formula meal. We found that prematurity and postcibal gastric acidity were significantly correlated with the amount of GER observed. Historical symptoms appeared to have little correlation with the amount of GER as measured by prolonged intraesophageal pH monitoring.