In this paper, the isolated influence of physical factors on the development of gastroesophageal reflux in man is analyzed by means of a mechanical model. We evaluate the influence of gravity, intraabdominal pressure, intrathoracic pressure, transmission of intraabdominal pressure to the high pressure zone, filling volume of the stomach, and the existence of a high pressure zone on the appearance of gastroesophageal reflux. PH-metry is used to record the episodes of reflux in the model. We wish to demonstrate the importance of gravity and intraabdominal pressure in the production of reflux. Intrathoracic pressure acts as an antireflux mechanism only when associated with a zone of high pressure. The intraabdominal pressure may be transmitted to the high pressure zone as a purely mechanical effect and the greater gastric filling volume may, when associated with the intraabdominal pressure, facilitate reflux without physical changes in the high pressure zone (the equivalent of a reduction in the length of the lower esophageal sphincter in man). We conclude that this model may help to explain the influence of the physical factors mentioned above on the development of gastroesophageal reflux in man.