Pancreatico-biliary diversion (PBD) by jejunal transposition in rats caused pronounced hyperplasia of pancreas. The increase of pancreatic trypsinogen contents exceeded the pancreatic growth, while pancreatic lipase and amylase contents relatively reduced. The high level of plasma CCK at the early period of PBD gradually decreased. The plasma secretin levels remained unchanged for 14 days after PBD. The plasma CCK levels were not elevated in fasting, but increased after intrajejunal infusion of 0.1 N HCl or Clinimeal. In acini prepared from PBD rats, the responsiveness to CCK8 was decreased when amylase release was expressed relative to DNA. The dose-response curve for CCK8 was shifted 3 fold toward higher concentrations of CCK8 4 days after PBD, but on 7 and 14 days after PBD returned to the same curve as the transected rats (control).