Endosulfan is widely used in insect control and it is absorbed by both humans and animals through ingestion, inhalation, and percutaneously. The purpose of this work was to study blood glucose levels and ultrastructural changes that might occur in the pancreas of adult male Wistar rats as a result endosulfan intoxication. The treated group (n = 60) received endosulfan orally via gavage 2.0 mg/kg per day in corn oil for 6 weeks, while the control group (n = 10) was given equal amount of corn oil for the same period. The substances were administrated once a day. Blood glucose levels were significantly increased at the end of 3rd and 4th week (P < 0.05), and 5th and 6th week (P < 0.01) after administration of endosulfan to rats compared with the control group. In electron microscopy studies, at the end of 2nd and 3rd weeks, swelling of mitochondria; at the end of 4th week, vacuoles in cytoplasm; at the end of 5th week, dissolution of mitochondrial matrix; and at the end of 6th week, picnotic nucleus in B cells in Langerhans islet were observed after endosulfan treatment. (C) 2004 Elsevier Ireland Ltd. All rights reserved.