Seventeen infants under 2 years of age with documented gastroesophageal reflux were studied by continuous distal esophageal pH monitoring and were compared to six age-matched control. Records obtained from patients with GER differed significantly from controls in the percent of monitored time with pH below 4.0, the number of episodes of reflux per monitored hour, and the duration of the longest episode of reflux. The differences between the groups became highly significant when the two-hour period after a clear liquid feeding was evaluated separately. Continuous monitoring of distal esophageal pH is a more sensitive and specific means of diagnosing GER than the diagnostic tests available at present.