The influence of longterm increase in the plasma CCK levels on beta-cell function in rats was studied by using the pancreatico-biliary diversion (PBD) model. An intravenous glucose load (800 mg glucose/kg) was performed three weeks after the PBD operation. Additionally a group of PBD operated animals as well as an unoperated group received the CCK receptor antagonist L364,718 continuously during the three week study period. The proliferation rate of endocrine pancreatic cells was studied by means of 3H-thymidine administration. PBD caused a decrease in basal levels of insulin and glucose and an augmented insulin secretory response after glucose injection. There was no appreciable influence on the glucose elimination rate. When PBD animals were given the CCK receptor antagonist no differences were observed with regard to insulin and glucose compared to PBD animals without antagonist. The CCK-antagonist did not influence the beta-cell function in unoperated animals. Further, the proliferation rate of the endocrine pancreatic cells was not significantly changed in the PBD rats. The results suggest that PBD is accompanied by significant changes in basal and stimulated insulin secretion. These changes are probably not a direct consequence of the increased plasma CCK levels that follows PBD. Moreover, the insulin secretory response to glucose in normal rats was not influenced by longterm administration of the CCK receptor antagonist. Our observations should encourage further studies on the complex entero-insular interactions following pancreaticobiliary diversion.