Malabsorption of bile acids is known to occur in patients with pancreatic insufficiency particularly when due to cystic fibrosis. Abnormal biliary secretion or intraluminal acidic precipitation of bile acids could contribute to the steatorrhea of pancreatic insufficiency. To measure bile acid outputs and duodenal concentrations of bile salts and lipids simultaneously, we performed intestinal intubation and perfusion studies during feeding of a solid test meal in 6 healthy controls and 8 adult patients with advanced acquired exocrine pancreatic insufficiency. The effects of various treatment regimens were also investigated. Postprandial bile acid secretion was similar in all treatment groups. However, significant (P less than 0.05) reductions in micellar concentrations of bile acids and fatty acids were observed in untreated pancreatic insufficiency. These abnormalities were directly related to pH-induced precipitation of bile acids and were corrected only by the addition of cimetidine to standard pancreatin therapy. Thus, in pancreatic insufficiency, treatment with pancreatin plus cimetidine enhances fat digestion and absorption by reducing both acid-peptic inactivation of lipase and acidic precipitation of bile acids.