The role of an antireflux procedure as an adjunct to esophagomyotomy fur achalusia remains a subject of controversy. Little objective documentation exists of this operation's effect on sphincteric competence and the degree of postoperative gastroesophageal reflux. This report of esophageal manometry and 24-hour pH monitoring on 14 patients with esophageal achalasia whom we had previously treated by a short esophagomyotomy without an antireflux procedure provides such documentation. Esophagomyotomy reduced lower esophageal sphincter pressure by 12% to 71% (mean 41%) from a preoperative mean of 26.7 mm Hg to a postoperative mean of 14.6 mm Hg. The number of postoperative episodes of acid reflux per patient in 24 hours was fewer than 29 (normal <49) in 13 patients, with a median of 12 episodes for the entire group. Esophageal acid exposure, measured as percentage of total time with pH less than 4.0 (normal <4.5%), was below 4.5% in 10 patients, six of whom had values less than 1%. Among the four patients with values greater than 4.5%, only one had a temporal correlation of symptoms with an episode of acid reflux. Multivariate analysis showed that esophageal acid exposure time correlated only with the level of residual lower esophageal sphincter pressure during the relaxation phase of deglutition. A pressure less than 8 mm Hg was predictive of normal acid contact time (p < 0.001). Mean lower esophageal sphincter pressure, percent reduction in lower esophageal sphincter amplitude, postoperative vector volume, and length of the lower esophageal sphincter did nut significantly correlate with amount of esophageal acid exposure. We conclude that a short esophagomyotomy without an antireflux procedure results in a competent lower esophageal sphincter in most patients. Increased esophageal acid exposure, when it occurs, is due to slow clearance of esophageal acid from relatively few reflux episodes and is more likely to occur when there is a high residual pressure during deglutition after myotomy. These findings suggest that the addition of an antireflux procedure to u short esophagomyotomy would nut be expected to improve clinical results.