The pressure and intra-abdominal length of the lower oesophageal sphincter (LOS) were measured by oesophageal manometry before and after floppy Nissen fundoplication (FNP) for intractable gastrooesophageal reflux. Control of reflux was assessed by 24 h pH recording and endoscopy. It was complete in 67 cases (84.8 per cent) in this non-consecutive series. In the group as a whole LOS pressure increased significantly after FNP, but the intra-abdominal length did not. LOS pressure decreased in 21 cases of whom 16 (76.2 per cent) still had perfect reflux control. Likewise, intra-abdominal length decreased in 41 cases of whom 36 (87.8 per cent) had good reflux control. There was no evidence of a compensatory increase in length to account for reflux control when LOS pressure decreased. When a length-pressure diagram was plotted for the postoperative measurements no clear separation of those with persistent reflux could be seen. These results suggest that the measured changes in LOS pressure and length following FNP are an artefact of surgery rather than the means by which the operation controls gastro-oesophageal reflux.