['Oesophageal pH monitoring is considered to be the gold standard investigation in the diagnosis of gastro-oesophageal reflux disease. Results of pH monitoring in regurgitating infants, however, may be within normal ranges. Therefore it was hypothesized that prolonged buffering of gastric acidity caused by milk-feeding may falsely normalize the pH data. Therefore, it may be relevant to omit the periods of gastric acid buffering in the analysis of the oesophageal pH monitoring data.', 'Combined gastric and oesophageal pH monitoring (Digitrapper Mark III, two-channel antimony electrode, Synectics) was performed in 90 consecutive infants, 0.5-10 months old, who were referred to the unit by outdoor paediatricians for pH measurement. The data were analysed in three different ways. The reflux index (RI), or the percentage time that the pH in the oesophagus was < 4.0, was calculated in three different ways: (i) the total duration of the investigation; (ii) excluding 90-min postprandial periods, starting from the beginning of a feeding; and (iii) excluding all periods with a gastric pH > 4.0, which are the periods of gastric buffering with a theoretical impossibility of recording an oesophageal pH < 4.0.', 'The mean duration of the pHmetries was 19.20+/-2.01h (A; mean +/- 1 SD), with a RI of 5.38+/-5.39% (B; median 3.45%). If the 90-min postprandial periods were not considered, the mean duration decreased to 12.21+/-2.41h (C; P(A vs C) < 0.001), with an oesophageal RI of 6.82+/-6.57% (D; median: 4.65; P(B vs D) = NS; r (B vs D) = 0.97). If all periods with a gastric pH > 4.0 were elminated, the duration available for analysis of the data with a gastric pH < 4.0 was 12.53+/-4.00 h (E; P(A vs E) < 0.001; P(C vs E) = NS), with an oesophageal RI of 7.06+/-7.52% (F; median: 4.50; P(B vs D vs F) = NS; r(B vs F), (D vs F) = 0.96).'] Does oesophageal pH monitoring in infants : elimination of gastric buffering modify reflux index?