For decades it has been supposed that emptying of the gall-bladder follows a rise in gall-bladder pressure of some 10-15 mmHg and relaxation of the sphincter of Oddi. 2. This subject has been re-examined in dogs chronically fitted with fistulas, using a model which does not entail interference with either the bile duct or sphincter of Oddi. 3. The pressure in the gall-bladder was recorded continuously under fasting conditions, after feeding and after intravenous infusion of the octapeptide of cholecystokinin (CCK-OP) in six dogs. 4. Gall-bladder pressure showed a modest sustained rise of 2-3 mmHg following ingestion of food and intravenous infusions of CCK-OP (125 ng kg-1 h-1). 5. During half of the experiments a transient rise of 3-10 mmHg lasting 2-3 min was observed after feeding and following infusion of I.V. CCK-OP (125 ng kg-1 h-1). Emptying of the gall-bladder, measured by bilirubin output from the biliary fistula, started shortly before the peak rise in pressure occurred. 6. We conclude that a significant rise in gall-bladder pressure is not a prerequisite for emptying and that the pressure changes occurring physiologically are smaller than have been reported previously. 7. We believe that the larger pressure changes recorded in the past may have been produced because of resistance to bile flow introduced by the models employed. 8. Emptying of the gall-bladder, in the dog, appears to have occurred within 40 min of the ingestion of food, suggesting that the cephalic and gastric phases of this process are quantitatively more important than has been thought previously.
