Under specially controlled conditions in the healthy unanesthetized dog we have measured the resistance offered to the flow of bile through the lower common duct. The average resistance 4 to 12 hours after a feeding was found to correspond to the pressure of a column of bile 100 to 120 mm. in height. After a 24 to 72 hour fast the resistance was such as to support a much higher column of bile, one of 300 mm. at times. The exhibition of food to the fasting animal usually precipitated a reflex lessening in the resistance to the flow of bile to the intestine, the actual taking of food always brought it about. This was transient and was soon followed by a period of increased resistance lasting 10 to 30 minutes after food had entered the stomach. There succeeded a drop in resistance which was gradual and fluctuating. We have observed an increase in the resistance to the flow of bile into the intestine after alkali has entered the stomach, and a decrease after acid has been administered. We attribute the sudden changes chiefly to the activity of the sphincter of Oddi.