To determine whether lower esophageal sphincter (LES) function was normal during early pregnancy, studies were performed in 8 pregnant women before and after abortion. Resting LES pressures were 22.1 +/- 2.4 and 22.6 +/- 2.3 mm Hg before and after abortion, respectively. During early pregnancy the LES pressure responses to pentagastrin were inhibited significantly. The LES responses to edrophonium and methacholine were decreased also. Finally, LES pressure responses to a protein meal were diminished in an additional 5 pregnant women. Serum concentrations of estrogen and progesterone were elevated during pregnancy, but the serum concentration of gastrin was unchanged. It can be concluded that in early pregnancy the basal LES pressure was within normal limits, but the LES pressure responses to hormonal, pharmacological and physiological stimulation were reduced (during demonstrated elevations of serum concentrations of estrogen and progesterone). These studies suggest that during early pregnancy, when no clinical symptoms of reflux are present, altered LES function may be demonstrated.