We analyzed the preoperative ambulatory 24 hour ph-metric and manometric characteristics in a group of 20 patients treated surgically for gastroesophageal reflux (PGER) by Nissen fundoplication. At 6 months post-surgery they were reevaluated instrumentally (manometric and 24 hour ph-metry) and clinically. All ph-metric parameters of PGER (total reflux time, clearance, number of episodes, number of episodes greater than 5 minutes duration and duration of longest episode) were significantly improved (p less than 0.01-0.05) post-operatively (as globally as by position supine and upright) and this improvement was associated with resolution of symptoms in 19 (95%) patients. Of the manometric parameters evaluated (lower esophageal sphincter pressure--LESP--and length--LESL, peristaltic, triphasic, biphasic, absent and simultaneous waves and relaxation of LES) surgery only produced improvement in the lower esophageal sphincter pressure (LESP) and length (LESL) (p less than 0.001). We conclude that antireflux surgery (Nissen) by improving the pressure and length of the LES is capable of producing clinical and ph-metric remission in almost all (95%) of patients studied six months after.