The aim of the present study was to investigate whether any differences could be demonstrated between patients with reflux symptoms and an acid-sensitive oesophagus (group I) (positive acid perfusion test) and a matched control group of patients with reflux symptoms and an acid-insensitive oesophagus (group II) (negative acid perfusion test) with respect to other oesophageal function tests (manometry, acid clearing and acid reflux (12-h continuous pH recording)). The two groups consisted of 47 and 46 patients, respectively. No differences were demonstrated between the two groups with respect to gastro-oesophageal sphincter pressure, acid-clearing ability, and acid reflux (irrespective of the criterion used for reflux). From the study it may be concluded that not only hydrochloric acid but other components of the reflux material may be responsible for producing symptoms of gastro-oesophageal reflux.