The role of abdominal musculature in the prolapse of esophagus and stomach into the buccal cavity during vomiting of the frog was studied. Vomiting of a normal frog produced by admmistration of a emetic, antimony potassium tartrate, was always accompanied by temporary prolapse of the esophagus and stomach into the mouth simultaneous to a strong contraction of the abdominal musculature. But a frog with a chronically denervated abdominal musculature failed to produce the prolapse of the esophagus and stomach, and expelling the food was senously prevented, even if the emetic was administered. This indicates that the prolapse, which is the indispensable behavior of vomiting act in frogs, is induced by the rise of intraabdominal pressure due to the strong contraction of abdominal musculature.