A comparison was made of the pre- and postoperative lower esophageal sphincter (LES) pressures in nine patients undergoing a posterior gastropexy for complicated gastroesophageal reflux. LES pressure was increased from 4.4 plus or minus 0.4 mm Hg to 13.9 plus or minus 0.5 mm Hg following surgery (p less than .01). The ratio of the change in LES pressure compared to the change in gastric pressure during increases in intra-abdominal pressure delta S/delta G, was 0.59 plus or minus 0.05 preoperatively and 0.94 plus or minus .01 postoperatively (p less than .01). All patients were asymptomatic after surgery. Both the resting LES pressure and the S/G ratio following surgery were significantly less than the comparable values obtained in an age-matched control population (p less than .01). These studies suggest that the clinical improvement following surgery for gastroesophageal reflux may be due to the increase in resting LES pressure and the improved response of the LES to increased intra-abdominal pressure.