The aim of the study is to compare the characteristics of reflux episodes in controls and in patients with various degrees of oesophagitis and Barrett's oesophagus. Ambulatory 24-h impedance-pH tracings were analysed from healthy volunteers, patients with non-erosive reflux disease (NERD), patients with grade A oesophagitis, grade B oesophagitis, grade C or D oesophagitis and patients with a short segment (<2 cm) of Barrett's metaplasia. The number of acid and weakly acidic reflux episodes increased from 25.9 +/- 3.9 to 17.9 +/- 1.5 in the controls, 39.9 +/- 6.3 to 33.4 +/- 5.7 in the patients with NERD, 46.6 +/- 6.2 to 40.4 +/- 9.2 in grade A, 68.2 +/- 9.2 to 49.2 +/- 12.3 in grade B, 79.8 +/- 15.6 to 47.4 +/- 4.6 in grade C/D and 75.1 +/- 7.9 to 37.3 +/- 8.5 in the patients with Barrett. The proportion of reflux episodes that is acidic or alkaline was similar all groups. Comparison with normal values revealed that none of the controls, 40% of the patients with NERD, 50% of the patients with grade A, 80% of the patients with grade B and all patients with grade C/D or Barrett's oesophagus had an abnormally high total number of reflux episodes. In the patients with severe oesophagitis a significantly higher percentage of reflux episodes reached the proximal oesophagus (43.8%) compared to the patients with Barrett's oesophagus (19.2%). With increasing degrees of oesophagitis, patients have more reflux episodes but a large overlap between the groups exists making comparison with normal values of limited relevance. In patients with Barrett's oesophagus fewer reflux episodes reach the proximal oesophagus which might explain their low sensitivity to reflux.