['An unbuffered pocket of highly acidic juice is observed at the gastric cardia after a meal in healthy subjects.', 'To compare the postprandial acid pocket in healthy subjects and patients with severe reflux disease and define its position relative to anatomical and manometric landmarks.', '12 healthy subjects and 16 patients with severe reflux disease were studied. While fasted, a station pull-through was performed using a combined dual pH and manometry catheter. Position was confirmed by radiological visualisation of endoscopically placed radio-opaque clips. The pull-through study was repeated 15 min after a standardised fatty meal. Barium meal examination was performed before and following the meal.', 'A region of unbuffered acid (pH <or=2) immediately distal to the proximal gastric folds was more frequent in reflux patients (23/32 studies) than in healthy subjects (11/24) (p<0.05). This unbuffered acid pocket was longer in the reflux patients than in the healthy subjects (median length 3 cm (range 1-15) vs 2 cm (range 1-5); p<0.05). The acid pocket extended proximally as far as the proximal gastric folds in the patients but stopped a median of 1.1 cm distal in healthy subjects (p = 0.005). In healthy subjects the acid pocket occupied the distal portion of the sphincter which opened postprandially, whereas in reflux patients it corresponded to the proximal displacement of the gastric folds--that is, hiatus hernia.'] Is severe reflux disease associated with an enlarged unbuffered proximal gastric acid pocket?