Two groups of newborns and infants with gastroesophageal reflux (GER) were retrospectively analyzed for the diagnostic accuracy and therapeutic guidance offered by extended intraesophageal pH monitoring. There were 28 patients in group I whose major presenting sign was recurrent pneumonia due to GER, and 22 patients in group II, with apnea caused by GER. The pH probe was 100% accurate in identifying the presence of GER. Barium esophagram was accurate 46% of the time. The pH probe accurately identified the appropriate mode of therapy in all patients. In the medically treated GER/Pneumonia group, the mean number of episodes of GER per 24 hours was 24, whereas in the surgical group the mean number was 63. Similarly, in the medically treated GER/Apnea group, the mean number of reflux episodes per 24 hours was 26, whereas the surgical group experienced 64. Had the pH probe been used to guide therapy, no patient would have been treated inappropriately. The number of patients in this report is not large. Prospective verification of these observations is required before this methodology can be utilized routinely in patients with GER.