The intestinal resorption of zinc using 65ZnCl2 was estimated in 3 patients with acrodermatitis enteropathica, 2 healthy controls, and 3 heterozygotes. After oral application of 65Zn the whole body activity was measured by a whole body counter for 34 days. The 65Zn resorption of the patients amounted to 16, 42 and 30% of the applied dose, whereas the resorption values of the heterozygotes and the controls were in the range of 58 and 77%. The elimination of 65Zn from the body amounted to about 0.7% of the applied dose with no difference between controls and patients with acrodermatitis enteropathica. Before therapy the serum-zinc levels of patients were markedly decreased. After oral application of high doses of zinc aspartate (2 times 400 mg/day) all clinical symptoms disappeared within a week. The results point at a causal connection between zinc and the pathogenesis of acrodermatitis enteropathica. Ultrastructural alterations of the Paneth cells of the intestines are also shown in this disease [12] as have also been seen in Paneth cells of zinc deficient rats [Beitr. Path. 145, 336 (1972)].