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