Bronchial asthma and acid reflux into the distal and proximal oesophagus. The prevalence of pathological gastro-oesophageal reflux in children and adolescents with asthma was studied by 24 hour two level oesophageal pH monitoring in 42 subjects aged 9-20 years with moderate or severe bronchial asthma. The importance of oesophagobronchial nerve reflexes and of aspiration of gastric acid as triggers in asthma was assessed by studying whether episodes of reflux into the distal and into the proximal oesophagus were followed by asthma attacks. Twenty-one subjects (50%) had a pathological total reflux time in the distal oesophagus and six (16%) in the proximal oesophagus. Nine patients had pathological gastro-oesophageal reflux into the distal oesophagus together with symptoms of asthma during the day on which the recording took place. In three of them the episodes of asthma symptoms were significantly correlated with preceding episodes of reflux into the distal oesophagus, and in one subject to reflux into the proximal oesophagus. We conclude that pathological gastro-oesophageal reflux is common in children and adolescents with asthma, but it seems to provoke symptoms of asthma in only a few. Symptoms of asthma were more often elicited by exposure of the distal oesophagus to gastric acid, possibly by a vagal reflex, than by aspiration of gastric juice. 