Some methodological in vitro observations concerning bile reflux monitoring (Bilitec) suggested that Bilitec monitoring is underestimating reflux in an acid environment. Moreover, other studies showed that the area above the cutoff level of bilirubin absorbance would provide an adequate quantitative marker for reflux of duodenal contents. Our aim was to study whether correction for intraesophageal acidity and the area above cutoff during Bilitec monitoring affects the results and the correlation with pH measurement and esophageal lesions. In 84 patients (46 men; mean age 46 +/- 2.7 years) evaluated for suspected gastroesophageal reflux disease, we performed ambulatory 24-hr esophageal pH and Bilitec monitoring after an upper gastrointestinal endoscopy. We obtained total area, percent total time, and correction by computer software. The correction factor for bilirubin absorbance was based on literature data for acidified bile (0.06 for pH < 3.6; 0.21 for pH < 2.6). Endoscopy revealed esophagitis grade 1-2 (E1-2) and 3-4 (E3-4) in 23 and 16 patients, respectively. A progressive increase of mixed (acid + bile) reflux occurred with increasing severity of endoscopic lesions (E3-4 vs no esophagitis, P < 0.05). A pathologic Bilitec monitoring result was present in the same 35 patients before and after correction and the correlation between the pH measurement and percent time of bile reflux was not improved by correction for intraesophageal pH (r = 0.386 and r = 0.391; P < 0.05). The total area of bilirubin absorbance above 0.14 (abs x min) was 7.8 +/- 2.2 in patients without esophagitis, and 11.7 +/- 4.4 and 17.0 +/- 4.2 in the E1-2 and E3-4 groups, respectively (E3-4 vs no esophagitis, P < 0.05). The correlation between the Bilitec monitoring and pH measurement regarding percent (r = 0.427, P < 0.01) or area of time below 4 (r = 0.280, P < 0.05) was not improved by considering the area of bilirubin absorbance above the cutoff level. Correction for intraesophageal pH has only a minor effect on the results of ambulatory Bilitec monitoring. Taking into account the surface rather than the percent of time above the cutoff level for bilirubin absorbance does not improve the correlation of Bilitec with acid reflux and with esophageal lesions.