Bile reflux has been implicated in the pathogenesis of Barrett's oesophagus but evaluation remains difficult. Bilitec 2000 is an ambulatory system that detects bilirubin based on its spectrophotometric properties. Oesophageal bile exposure was evaluated in three groups of patients. Group 1 (n = 11) were normal controls, group 2 (n = 13) were patients with uncomplicated gastro-oesophageal reflux and group 3 (n = 12) were patients with Barrett's oesophagus. Bile reflux was greater in patients with Barrett's mucosa than in controls or those with uncomplicated reflux. This difference was seen in the supine and interdigestive periods. The percentage of time at which gastric pH was greater than 4 and oesophageal pH was above 7 did not differ between the groups. Bilitec 2000 detects greater bile reflux in patients with Barrett's oesophagus. No corresponding gastric or oesophageal alkaline shift is found. This ambulatory bile reflux monitoring system may be a useful tool in clinical practice.