Zinc metabolism in 20 patients with stable type II diabetes mellitus was investigated. Twenty-five percent of these patients had depressed serum zinc concentrations, and all demonstrated hyperzincuria. Urinary zinc loss was greater when proteinuria was present and correlated with the mean serum glucose concentration. Studies of gastrointestinal zinc absorption suggested zinc malabsorption in patients with type II diabetes mellitus. Glucose infusion in normal dogs produced hyperzincuria without a diminution in serum zinc. It is concluded that hyperzincuria, resulting from a glucose-mediated process that is not osmotic, interacts with impaired zinc absorption to produce zinc deficiency in patients with type II diabetes mellitus.