Well-defined areas of the mesentery were superfused during 3 s with 300 microliters of hypertonic NaCl solution, while monitoring the electrophysiological response of the hypothalamo-neurohypophysial tract. Response magnitudes were largest for superfusion of the portal, the duodenal and jejunal mesenteric veins, and least for superfusion of the mesenteric vessels of the ileum. The results suggest the existence of peripheral receptors that appear to be strategically located to monitor the intestinal absorption of salt or water.