The explanation as to why gastroesophageal reflux disease develops remains unanswered. We have learned much about the regulation of LES pressure, the single most important factor in the development of reflux disease. Our understanding of factors involved in the clearance of refluxed contents has also increased. The presence of reflux in the postprandial period and with belching suggests that it is serving a physiologic function. This may be a response to increases in gastric volume or pressure accompanying these situations. The question that has not been satisfactorily answered is what factor is responsible for the progression of a physiologic phenomenon to a pathologic condition. The answer to this question lies in the development of more physiologic techniques for monitoring LES pressure changes and a better understanding of the neural and hormonal pathways that regulate lower esophageal sphincter tone.