Endoscopy, esophageal manometry and pH monitoring, gastric emptying test, and heartburn quantification on a visual analog scale were performed in 22 achalasic patients in order to clarify which events are associated with pathological esophageal acidification after successful LES dilatation. Five patients presented pathological acidification. Dilatation reduced LES tone from 38.3 +/- 4.2 to 14.6 +/- 1.1 mm Hg (mean +/- SEM); there was, however, no difference between nonrefluxers and refluxers (14.8 +/- 1.2 vs 13.8 +/- 2.5 mm Hg). The emptying time in achalasic patients was delayed compared to controls (315.9 +/- 20.9 min vs 209 +/- 10.4) due to prolonged lag-phase and reduced slope of the antral section-time curve, but, again, there was no difference between refluxers and nonrefluxers. The acid clearance was delayed in refluxers compared to nonrefluxers (15.9 +/- 4.5 vs 2.5 +/- 1.8 min, P<0.05). Two refluxers presented grade 1 esophagitis; one of them developed an esophageal ulcer. The heartburn score was the same in refluxers and nonrefluxers. Pathological acidification after pneumatic dilatation is associated with persistent problems in esophageal emptying rather than with excessive sphincter divulsion.