Esophageal and gastric tone was recorded in six pregnant and six nonpregnant women by means of a new technique for intraluminal pressure recordings. The recordings were performed in supine and standing positions, at rest, and during swallowing of saliva or water. It was found that the pregnant women had lower intraesophageal pressures but higher intragastric pressures compared to the nonpregnant women. In one of the pregnant women a negative pressure situation was recorded between the stomach and lower esophagus. This patient also complained of severe heartburn when she was lying down. Gastroesophageal reflux seems to be aggravated in pregnant women since esophageal peristalsis in these patients has lower wave speed and lower amplitude compared to nonpregnant women.