The role of endogenous cholecystokinin (CCK) in stimulating hepatic bile flow was evaluated. Attention was directed at discerning the relative importance of the ability of CCK to stimulate the release from the pancreas of the choleretic hormones glucagon and insulin. Utilizing dogs with chronic biliary and gastric fistulas, duodenal infusion of a lipid emulsion resulted in an increase in cholecystokinin concentration and hepatic bile flow. Endogenous CCK stimulation was associated with a significant increase in the concentrations of both glucagon and insulin. In an effort to separate the potential choleretic response of CCK from that of glucagon and insulin, subsequent experiments were performed on anesthetized dogs that had the source of glucagon and insulin eliminated by pancreatectomy and gastrectomy. The duodenum and its arterial blood supply and venous drainage were carefully preserved, and intraduodenal infusion of emulsified lipid resulted in an exaggerated increase in systemic CCK concentrations. Although CCK release occurred in the absence of the pancreatic and gastric changes in bile flow, glucagon and insulin were eliminated. The results of this study indicate that intraduodenal lipid increases hepatic bile flow by glucagon- and insulin-mediated CCK stimulation. There is no evidence to support any direct choleretic activity of CCK.