The intravenous administration of octreotide stimulates sphincter of Oddi activity and impairs pancreatic flow into the duodenum. Postsecretin ultrasonography (US-S test) has revealed an increase in the caliber of the main pancreatic duct, which disappears in healthy persons approximately 10 minutes later as a result of the opening of the sphincter of Oddi and passage of stimulated fluids into the duodenum. We have assessed US-S test patterns after octreotide in healthy persons and in patients with recurrent acute pancreatitis. The study sample consisted of 16 participants: alcohol-abstinent, nonsmoking, healthy volunteers (four men, three women; mean age: 28 ± 2.5 years) and nine patients with recurrent acute pancreatitis (six men, three women; mean age: 32.1 ± 7.1 years). All participants underwent measurement of the main pancreatic duct at 1-min intervals for 60 min after secretin stimulation (1 IU/kg intravenous bolus). On a different day the same persons had repeated US-S tests 1 hour after administration of 0.1 mg octreotide intramuscularly. In both controls and patients with recurrent acute pancreatitis, octreotide administration induced an appreciable dilatation of the main pancreatic duct before secretin stimulation, and the caliber remained significantly increased throughout the duration of the test. These results suggest that a single administration of octreotide at the dose used (a) does not inhibit pancreatic secretion of basal and secretin-stimulated fluid within the first 60 min and (b) probably exerts an inhibitory effect on sphincter of Oddi relaxation. These findings warrant more intensive study given their therapeutic implications for acute pancreatic disease.