Three manometric characteristics of the distal oesophageal sphincter (DOS; pressure, length below the respiratory inversion point, i.e., abdominal length, and overall length) were investigated in 10 healthy volunteers and in 66 patients with typical symptoms of gastro-oesophageal reflux (GOR) disease. The aim of the work was to correlate the DOS deficiency with symptoms, endoscopic oesophagitis and with specific patterns of GOR as determined by means of 24-hour oesophageal pH monitoring. The results showed that patients with and without GOR disease cannot be separated solely on the basis of the standard manometric test, even adopting more parameters besides the traditional DOS pressure measurement. A functional defect of the DOS may be hypothesized for those patients with an apparently normal DOS on standard oesophageal manometry.