In scanning patients for Meckel's diverticulum, the colon occasionally visualizes more rapidly than would be expected simply from gastric secretion and intestinal transit. To gain a better understanding of the intestinal physiology of pertechnetate and thereby to make a more intelligent interpretation of abdominal scans, segments of the gastrointestinal tract of Sprague-Dawley rats were isolated by transection between double ligations. After abdominal closure, the animals received an intravenous injection of 99mTcO4 and were killed at 30, 45, or 150 min after injection. Technetium concentrations in the stomach, colon, and appendiceal contents increased significantly with time after dosing, and after 30 min technetium could be clearly imaged in the stomach, upper small intestine, appendix, and colon. These results suggest that technetium is actively secreted by the intestinal mucosa. Additionally, the results indicate caution in the interpretation of scans in patients with suspected Meckel's diverticulum since, in the rat and probably in the human, significant amounts of technetium can accumulate in the gut apart from gastric secretion and intestinal transit.