Electromyography of 12 clinically normal dogs and 7 dogs with idiopathic megaesophagus revealed trains of positive sharp waves in the muscles of facial expression and in the lingual muscles of both groups. Positive waves are usually indicative of motor-unit disease; however, they are clinically insignificant in these muscles. Positive sharp waves were detected in the esophageal muscle of one dog with congenital megaesophagus. Esophageal electromyograms obtained in a dog with congenital megaesophagus and in 2 clinically normal dogs were normal. Resting caudal esophageal sphincter pressure was similar in both clinically normal dogs (mean, 22.3 mm of Hg; range, 15--37 mm of Hg) and in dogs with congenital or acquired idiopathic megaesophagus (mean, 29.6 mm of Hg; range, 20--50 mm of Hg).