The present knowledge regarding esophageal function was critically reviewed and the mechanism of the transportation of the content in the esophagus was further investigated in the dog. Secondary peristalsis is present throughout the entire length of the esophagus, and the threshold for its initiation is higher in the cervical than in the thoracic portion. There is probably a common set of efferent fibers for both the primary and secondary peristalsis of the esophagus. Afferent fibers for the secondary peristalsis of the thoracic portion of the esophagus are present in the vagus nerves together with the motor fibers. Specific afferent fibers for the secondary peristalsis of the cervical portion of the esophagus may be found in the communicating branch between the inferior and superior laryngeal nerves. The secondary peristalsis of the esophagus, like the primary, is under central control. Successive peripheral stimulations causing a chain of reflexes are normally present but are not necessary for its maintenance. Secondary peristaltic activity of the upper segment of the esophagus had an inhibitory effect on the similar activity of the lower segment. This inhibitory effect of the activity of the upper part on the lower part from the pharynx to the cardia and fundus of the stomach may be the most important central mechanism of the polarity and efficiency of esophageal peristalsis. The primary peristalsis of the esophagus is apparently not different from the secondary peristalsis regarding the speed of progress, the force of propulsion and the ability to jump over a gap. In the normal physiological process of deglutition both the secondary and primary peristalsis play an important role.