Relations between primary oesophageal peristaltic amplitude and traction force were studied in 30 normal volunteers, 12 patients with functional dysphagia, and 48 patients with gastro-oesophageal reflux disease, using a new intraluminal strain gauge device. Forces generated by swallowing in the normal oesophagus were 42 (35-60) g (median and interquartile range), a close positive correlation existing between traction force and contractile amplitude for each subject (r = 0.5 (0.38-0.6). Traction force increased with increasing balloon volume from 62 (50-73) g at 2 ml to 86 (70-105) g at 4 ml (p < 0.05), indicating distension related modulation of peristaltic force. Patients with oesophagitis generated lower traction forces on swallowing 30 (20-40) g compared with the normal subjects (p < 0.01), the degree of impairment being greatest in those patients with the most severe mucosal damage. Patients with gastro-oesophageal reflux without endoscopic oesophagitis also showed abnormal forces (32 22-38) g p < 0.01 v controls), which were similar to those patients with mild oesophagitis but were greater than those with severe oesophagitis (p < 0.05). In patients with functional dysphagia, forces were also impaired (28 (10-60) g p < 0.05 v controls) despite normal standard manometry. Our results show that measurement of the traction force generated by primary peristalsis provides information about oesophageal neuromuscular function that is not demonstrable by manometry alone and can be abnormal in patients with oesophageal symptoms in whom standard techniques are normal.