The diagnosis of esophageal rupture in ballon dilatation is usually made from clinical symptom of sharp chest pain, plain chest radiographs and esophagograms after dilatation. It has some problems ; the pain is varied patients to patients and bacterial flora in the mouth or esophagus can be mixed with the contrast media to flow into the mediastinum during esophagography, to create mediastinitis. We could make the diagnosis of esophageal rupture without using contrast media by the observation of the pressure change in the ballon during dilatation An infusion pump, transducer and esophageal balloon were connected through a multi-way connector, and the transducer of them was also connected to an amplifier which was connected to a pressure monitor to record the balloon pressure. A balloon(20m./3cm) inserted in the mid-thoracic esophagus under the fluoroscopic control was inflated until the esophagus was ruptured. Balloon was distended by injecting air in 15 rabbits(A group), and b injecting diluted contrast medium in 15 rabbits(B group). The pressure decrease after esophageal rupture was ranged from 94 to 160mmHg(mean ; 103) in A group and 340 to 1040 mmHg(mean ; 537 ) in B group. The pressure curve of A group was smooth, regular and so accurate to make the diagnosis of esophageal rupture, whereas that of B group was irregular and not so accurate. In conclusion, our new method to make the diagnosis of esophageal rupture during balloon dilatation may be useful in patients of esophageal stricture.