To avoid food impaction artifacts during ambulatory bile reflux monitoring (Bilitec), some groups have allowed only a liquid diet, while others omitted the meal and postprandial periods from the analysis. Our aim was to study whether Bilitec monitoring requires the use of a liquid diet. In 40 healthy subjects and 211 consecutive patients evaluated for suspected gastroesophageal reflux disease, we performed ambulatory 24-hr esophageal pH and Bilitec monitoring. The subjects were randomized to either solid or liquid meals during the procedure. All patients underwent an upper gastrointestinal endoscopy. In healthy subjects, liquid and solid diets were followed by similar acid exposure of the distal esophagus. During bile reflux monitoring, major meal artifacts occurred in 19% of the patients using solid meals, but in none of the patients using liquid meals. With liquid meals, but not with solid meals, a progressive increase in duodenoesophageal reflux occurred with increasing severity of endoscopic lesions. With liquid meals, but not with solid meals, the prevalence of pathological exposure to duodenoesophageal reflux increased with increasing severity of endoscopic lesions. With liquid meals, the results of pH monitoring and bile reflux monitoring correlated better than with solid meals. Thus, ambulatory Bilitec monitoring requires the use of liquid meals, as the use of solid meals is associated with too many meal artifacts and a poorer correlation with acid reflux and severity of endoscopic lesions.