Zinc concentration of the intestine, zinc-65 uptake by the intestine and zinc-65 absorption were measured in control and zinc-deficient rats. As zinc deficiency progressed, zinc concentration of the intestinal mucosa decreased whereas both the amount of zinc-65 taken up by the mucosa and the absorption of the isotope increased. In addition, zinc concentration of the plasma was decreased in zinc-deficient animals. When zinc-deficient rats were injected with ZnCl2 prior to oral administration of zinc-65, the zinc concentration of both the plasma and the intestine increased and there was a concomitant decrease in both zinc-65 uptake by the intestine and absorption of the isotope. The results of these experiments suggest that zinc absorption is regulated, in part, by the zinc content of the intestinal mucosa which, in turn, is regulated by the zinc content of the plasma.