The cutoff limit for pathologic gastroesophageal reflux (GER) has been arbitrary, although generally accepted determined at pH 4.00. The influence of a small pH error (0.25 pH units above or below pH 4.00) was analyzed in 173 consecutive pH monitorings. This appeared to cause a misinterpretation of the data in 51 of 173 infants (29%). We propose the introduction of a new parameter measuring the percent of time of the total investigation that the recorded pH varies between 4.25 and 3.75: the "oscillatory index" (OI). The index ranged from 0-42%. The higher the OI, the more pH data that are recorded between pH 4.25 and 3.75. The OI is related to the arbitrary aspects of a boundary level. The Pearson correlation coefficient between the percent of time of the investigation the pH was less than 4.00 and the OI was 0.75. If an OI of more than 10% in infants with normal pH-monitoring data of more than 15% in infants with a GER pathology would be considered as abnormal, pH-monitoring data of 45 infants should be considered for reclassification (26%). Prior to general application, this parameter should be evaluated by more centers in different patient populations, and other "oscillatory ranges" should be analyzed.