We have investigated in stimulated human pancreatic juice the presence of the following peptides: insulin, glucagon, gastrin, somatostatin, VIP and secretin. Collection of pancreatic juice (3 periods: 20 min each) was completed by endoscopic cannulation of the pancreatic duct during the infusion of secretin (0.5 U/kg/h) and cerulein (75 ng/kg/h) in 6 healthy volunteers. Pure pancreatic juice was recovered in the presence of kallikrein inhibitor (iniprol 8,000 U/ml) in refrigerated collection tubes (4 degrees C). The material was acidified, boiled for 5 min and centrifuged. Radioimmunoassays were performed on the supernatant solutions. The elution profiles on Sephadex G 25 gel filtration of the immunoreactivities were compared with standard samples of hormones, immuno-reactive insulin, glucagon and somatostatin were found in every sample: insulin was present at a constant level (50 microU/ml) during the three periods of collection; glucagon was encountered in large amounts in the first sample and decreased significantly during the subsequent periods; somatostatin which occurred at a low level during the first period was significantly increased in the following periods. Gastrin, VIP and secretin were undetectable or only inconstantly found in very small amounts. These results are in agreement with a two-directional secretion of the human pancreatic endocrine cells. The cellular origin and function of these exocrine secreted peptides need further studies.