The effects of varying loads of intraduodenal phenylalanine on pancreatic and gallbladder function were investigated in 32 healthy volunteers using a triple lumen perfusion system. L-phenylalanine absorption rates in the proximal jejunum were measured simultaneously. Intraduodenal L-phenylalanine produced a dose related increase in pancreatic secretion reaching the maximum at the concentration of 100 mM. Bilirubin outputs too increased significantly but did not parallel enzyme secretion. In contrast to the effect of L-phenylalanine, D-phenylalanine 50 mM did not stimulate pancreatic enzyme secretion and gallbladder emptying. The absorption rates of L-phenylalanine increased with rising luminal concentrations. There was a significant correlation between pancreatic secretion and L-phenylalanine absorption rates. This relationship suggests that the release of cholecystokinin, a hormone stimulating pancreatic and biliary function is dependant of the absorption of nutrients like amino acids.