Jejunal electrolyte absorption was measured in the jejunal loops of anesthetized dogs during infusions of hypertonic solutions via the portal vein. The net Na absorption was not influenced by the 9% NaCl infusion into the inferior vena cava, although it was significantly attenuated by the portal 9% NaCl infusion. This effect may not be due to the osmotic stimulus, since the portal 50% glucose or 6.5% LiCl infusion had no significant influence on the net Na absorption. To determine the mechanism of the decrease in the net Na absorption during the portal hypertonic NaCl infusion, the net Na absorption was measured after the section of anterior and posterior hepatic nerves (SAPH) or intravenous atropine injection. Both SAPH and the intravenous atropine injection completely blocked the effect of the portal 9% NaCl infusion on the net Na absorption. These results indicate that 1) net Na absorption in dog jejunum is depressed by the hypertonic NaCl infusion via the portal vein; 2) the effect is NaCl specific and may not be due to the osmotic stimulus; and 3) the afferent limbs of this effect are the anterior and posterior hepatic nerves, and the efferent limb of this effect is the vagus nerve. Thus the hepatojejunal reflex may play an important role in the regulation of body fluid homeostasis.