This study was conducted to determine if different anatomical sites within the peritoneal cavity have different capacities for portal insulin absorption. Diabetic male Sprague-Dawley rats were studied. They were anesthetized and injected with streptozotocin. Blood glucose was measured before and after insulin (1 U/kg) was applied directly to the omentum, serosal surface of cecum, or parietal peritoneum or injected subcutaneously. In a control group, blood glucose was measured at intervals without administering insulin. In addition, insulin labeled with radioactive iodine (125I) was applied to the same three locations in the peritoneal cavity or injected intravenously. Animals were sacrificed at 1, 5, 15, or 30 mins, and radioactivity was measured in excised livers and in blood samples. Blood glucose in the omental group responded to insulin with a greater hypoglycemic effect than in the peritoneal and control groups. The percentage of radioactivity recovered in liver was significantly higher in the omental than in the serosal and peritoneal groups at 1 and 5 mins. The ratio of liver-to-blood radioactivity was also significantly higher in omental than in serosal and peritoneal groups and higher in the serosal than in the peritoneal group at 5 mins. The data suggest that, in this model, the omentum is a better site for insulin absorption than serosa or parietal peritoneum and that significant portal venous absorption of insulin occurs.