The effect of fundoplication on patterns of gastro-oesophageal reflux and the underlying motor mechanisms were investigated in 18 patients with symptomatic reflux. Oesophageal motility and pH were recorded concurrently after a standard meal. Studies were performed preoperativey and from 5 to 27 months after surgery. Fundoplication virtually eliminated reflux in all but three patients. Control of reflux was associated with a 50% fall in the number of transient lower oesophageal sphincter relaxations, a fall in the proportion of transient lower oesophageal sphincter relaxations accompanied by reflux from 47% to 17%, and an increase in the mean residual pressure at the gastro-oesophageal junction during swallow induced lower oesophageal sphincter relaxation from 0·7 mm Hg to 6·0 mm Hg. Basal pressure at the gastro-oesophageal junction rose from 10·9 mm Hg to 14·5 mm Hg, however, there was no correlation between postoperative reflux and basal gastro-oesophageal junction pressure. These findings suggest that the antireflux effects of fundoplication result from changes in the mechanical behaviour of the gastro-oesophageal junction that result in incomplete abolition of the high pressure zone during lower oesophageal sphincter relaxation, and reduced triggering of transient lower oesophageal sphincter relaxations.