The importance of zinc for human health was first documented in 1963. During the past 25 y, deficiency of zinc in humans due to nutritional factors and several disease states has now been recognized. The high phytate content of cereal proteins is known to decrease the availability of zinc, thus the prevalence of zinc deficiency is likely to be high in a population consuming large quantities of cereal proteins. Alcoholism, malabsorption, sickle cell anemia, chronic renal disease, and chronically debilitating diseases are now known to be predisposing factors for zinc deficiency. A spectrum of clinical manifestations ranging from mild to severe degree have now been recognized in human zinc-deficiency states. Zinc is required for many biological functions including DNA synthesis, cell division, and gene expression. It is required for the activity of many enzymes in biological systems. Recent studies indicate that zinc is needed for cell-mediated immunity.