Six patients with known achalasia were examined by endoscopic ultrasonography before dilatation therapy. At the level of the lower esophageal sphincter, a typical enlargement of the echolayer corresponding to the muscularis propria was observed in 5 cases. Endoscopic ultrasonography is a complementary procedure to manometry and x-ray for diagnosing achalasia. It helps differentiate achalasia from pseudoachalasia. In pseudoachalasia there is tumor infiltration.