The present study was performed to investigate a possible influence of the adrenergic nervous system on pancreatic exocrine secretion stimulated by intraduodenal acid perfusion. Pancreatic secretion was collected in rats anesthetized with urethane after 24 hours fasting. The duodenal lumen was perfused (0.2 ml/min) with HCI solution in a concentration of 0.005, 0.01, 0.02, 0.05 or 0.1 N When the volume of panceratic juice secreted for IS min became constant phentolamine (1 mg/kg), noradrenaline (10 μg/kg), Propranolol (1 mg/kg), and isoproterenol (1 μg/kg) were administered through the jugular vein in bolus. The secretory volume and protein output were measured in the pancreatic juice collected for 15 min. 1) HCI, perfused intraduodenally in graded concentrations from 0.005 N to 0.1 N, increased the pancreatic secretory volume and protein output dose-dependently. 2) In the basal state as well as in the stimulated state by the duodenal acid perfusion, phentolamine increased the pancreatic secretory volume and protein output while propranolol inhibited the volume and protein output. 3) In the basal state, noradrenaline did not change the pancreatic secretory volume but increased the protein output while isoproterenol increased both of the secretory volume and the protein output. These results strongly suggest that α-adrenoceptors in the rat pancreas exert an inhibitory influence on the pancreatic exocrine secretion including volume and protein output in the basal state as well as in the stimulated state by the intraduodenal acid perfusion while β-adrenoceptors play a stimulatory role in the pancreatic exocrine secretion. However, in the physiological situation, adrenergic excitation may stimulate the protein output through β-adrenoceptors without change in the secretory volume in the rat pancreas.