Intraoperative electron beam radiotherapy (IORT) is clinically used as a potential adjunctive treatment to surgery of locally advanced pancreatic and gastric cancer. The tolerance of the pancreas to IORT was studied in 15 adult beagles, divided in 3 groups of 5 beagles in which 25, 30 or 35 Gy IORT was delivered through a 6-7 cm circular lucite cone with 6-8 MeV electrons to the pancreas and medial wall of the duodenum. The dogs were followed for endocrine and exocrine pancreatic insufficiency. Two dogs (13%) developed radiation-induced morbidity which consisted of a common bile duct stenosis and an enterocolic fistula, as was confirmed at autopsy after 8 and 18 months, respectively. After a follow-up of 1 year, none of the dogs had developed pancreatitis, diabetes or exocrine insufficiency. There was a significant reduction in serum insulin levels and glucose clearance rates without overt diabetes for 30 Gy and 35 Gy (p < 0.05). No significant changes were found for 25 Gy. This study suggests that 25 Gy IORT to the pancreas may be used clinically, and that higher IORT doses may induce endocrine pancreatic insufficiency in the long-term.