Intraluminal gastroesophageal pressure and pH studies have been performed on 8 nonpregnant women, 10 pregnant women with heartburn, and 10 pregnant women without heartburn. Each patient was tested under resting conditions and after intravenous injection of 0.6 mg atropine. In both groups of pregnant patients the intragastric pressure was found to be higher than that of the nonpregnant subjects. The stomach to lower esophageal sphincter pressure (LESP) gradient under resting conditions was least in the pregnant patients with heartburn. After the administration of atropine, a fall in the LESP occurred in all 3 groups of patients which was most profound in the nonpregnant subjects and in the pregnant patients without heartburn. These changes and the pH recordings of the lower esophagus indicate the adverse effect that atropine has on the competency of the LESP both in pregnancy and in the nonpregnant state. Atropine should therefore be used with caution as a premedicant and preferably combined with metoclopramide (Maxolon).