The role of cholinergic mechanisms in the control of gallbladder emptying has not been defined. In this report a scintigraphic technique using 2,6-dimethylphenylcarbamoylmethyl iminodiacetic acid labeled with technetium 99m to visualize the gallbladder and its emptying and diethylenetriamine pentaacetic acid labeled with indium 111 to visualize the stomach and its emptying was used to study 43 normal subjects and 18 patients with vagotomies. Direct cholinergic stimulation with bethanechol induced significant gallbladder emptying. Cholinergic blockade with atropine sulfate decreased the gallbladder emptying responses to a liquid meal, a solid meal, and the infusion of cholecystokinin-octapeptide. In patients with vagotomies, gallbladder emptying was decreased despite accelerated gastric emptying of an ingested liquid meal. The gallbladder emptying response to cholecystokinin-octapeptide was augmented in patients who had undergone vagotomy. These studies suggest that cholinergic receptors may be important in the regulation of human gallbladder emptying.