Insulin release, glucose utilisation and lactate production were investigated using an in vitro perfused rat intestine-pancreas preparation after intraluminal or arterial glucose administration. In the absence of intraluminal glucose administration, both glucose utilisation and lactate production seem to be dependent on the arterial glucose concentration. Despite the different proportions in the portal values of glucose and lactate found at the various arterial glucose concentrations, the percentage of the total carbon atoms from infused glucose recovered in the portal vein remained constant. A significant (p less than 0.01) increase in insulin secretion was observed when the arterial glucose concentration was increased from 5.5 to 16.7 mmol/l. After intraluminal administration of glucose (4 g/kg body weight) both as a bolus or as an infusion, the lactate produced and the insulin released by the preparation were not significantly increased with respect to values measured in the absence of intraluminal glucose load. After intraluminal administration of glucose (1 g/kg body weight) as a bolus, the net translocation of glucose from the lumen to the vascular circuit was apparently reduced when the glucose concentration was increased in the perfusate from 2.75 to 11.0 mmol/l; this reduction could be dependent on an increase in the metabolism of absorbed glucose. In conclusion, the functional unit intestine-pancreas seems to play an important role in glucose homeostasis by elaborating the adequate mixture of glucose and lactate that must reach the liver under the various metabolic conditions.