The gallbladder and gut should be viewed as hormonally responsive organs the normal physiology of which may be altered by the hormones of pregnancy. The gallbladder enlarges and empties sluggishly in response to meals during pregnancy. Small bowel transit is slowed, and the resting pressure of the lower esophageal sphincter is reduced. All these effects are reversed by delivery; motility reverts toward normal in the postpartum period. The rapid return of normal motility suggests that the effects of pregnancy are hormonally related. Most studies have demonstrated that progesterone, not estrogen, may be the hormone responsible. Although incompletely defined, one mechanism of the effects of pregnancy on motility may be progesterone-induced inhibition of the mobilization of intracellular calcium within smooth muscle cells.