The aims of this study were to assess the effect of pneumatic dilation on gastroesophageal reflux in achalasia, differentiate esophageal acid due to lactate from acid due to gastroesophageal reflux, and determine if chest pain and heartburn are reliable indicators of gastroesophageal reflux. Eight untreated achalasia patients underwent pre- and postdilation esophageal fluid/food residue lactate and pH analysis, esophageal manometry, 24-hr pH monitoring, and symptom assessment. All patients had a successful clinical outcome and a decrease in lower esophageal sphincter pressure from 29.1 +/- 12.7 to 14.7 +/- 3.8 mm Hg (mean +/- SD; P = 0.04). Abnormal acid exposure was present in two patients before and two patients after dilation. Postdilation acid exposure was mild. Lactate was detected before dilation in all patients. A lactate concentration >2 mmol/liter was associated with acidic residue and one abnormal 24-hr pH profile. There was no correlation between an abnormal 24-hr pH test and age, lower esophageal sphincter pressure, or duration of symptoms prior to treatment. Chest pain and heartburn were unrelated to drops in pH. Gastroesophageal reflux is rare in untreated achalasia and esophageal acidity may result from ingestion of acidic foods or production of lactate. Mild gastroesophageal reflux occurs after dilation but is of no clinical significance. Chest pain and heartburn are not indicators of acid reflux in achalasia.