Gallstones and sphincter of Oddi dysfunction are both more common in women than men, suggesting that endogenous hormones may play an important role in these conditions. Female sex hormones are known to affect cholesterol metabolism and gallbladder motility. However, the effect of these hormones on the sphincter of Oddi has not previously been studied. We therefore tested the hypothesis that exogenous estrogen administration would inhibit sphincter of Oddi motility. Twenty-three male prairie dogs fed a nonlithogenic diet were studied. Under alpha-chloralose anesthesia, a side hole pressure-monitored perfusion catheter was positioned in the sphincter of Oddi and perfused with degassed water at 0.15 ml/min. Femoral arterial and venous catheters were placed. Sphincter of Oddi phasic wave frequency (F), amplitude (A), and motility index (MI = F x A), as well as arterial blood pressure (BP), were monitored for 10-min intervals before (control), during 20-min intravenous infusions of 0.1, 1, or 10 micrograms/kg beta-estradiol, and for 20 min after estradiol infusion. No response was observed at the 0.1- or 1-micrograms doses. Sphincter of Oddi motility was significantly (P < 0.05) reduced during estrogen infusion at the higher dose of 10 micrograms, primarily due to decreased phasic wave frequency. Sphincter motility remained depressed for at least 20 min following estrogen infusion. We conclude that estrogen effects on the sphincter of Oddi may contribute to the higher incidence of gallstones and sphincter dysfunction seen in premenopausal women.