The effects of an altered pathway of bile flow upon fat metabolism and gastrointestinal hormone release were investigated in patients undergoing biliary reconstruction procedures or external biliary drainage. After ingestion of a fat-enriched meal, patients with jejunal interposition hepaticoduodenostomy showed the same patterns as controls, with similar levels of plasma triglyceride and gastrointestinal hormones. On the other hand, patients with Roux-Y hepaticojejunostomy or external biliary drainage revealed the impairment of fat metabolism, although the response patterns were different. As for the changes in gastrointestinal hormones in the two groups, both gastric inhibitory polypeptide (GIP) and insulin levels were reduced, whereas glucagon-like immunoreactivity (GLI) levels rose, especially in the external biliary drainage group. It is considered that the disturbance of fat metabolism, in cases of internal or external biliary diversion, is closely related to change in GIP, insulin, and GLI release, in addition to the impairment of mixed micelle formation by bile and of hydrolysis by pancreatic enzymes.