Yield pressure at the cardia was measured before and after fundoplication in 10 patients; five had a Nissen fundoplication and five a Belsey mark IV procedure. Surgery was considered successful if oesophagitis healed or if 24 hour pH monitoring returned to normal. There was a marked rise in yield pressure in all eight patients with a successful operation. Yield pressure remained low in two patients in whom oesophagitis persisted.