Zinc takes part in the catalytic function of many metalloenzymes. In others it plays a role in conformational stability. In zinc deficient animals protein synthesis is disturbed. Conversely zinc metabolism is influenced by protein deficiency. Zinc takes part in drug metabolism, in mobilizing vitamin A from the liver, and in a system defending the organism against free radical damage. Zinc distribution in the organism is influenced by steroid hormones and leucocytic endogenous mediators. Of the intracellular zinc only a small part is bound to metalloenzymes, most being coordinated to binding sites of nonspecific proteins. Thus the organism defends itself against conformational changes of irritable enzymes which may bind excess zinc to side chains. Zinc can protect the organism against cadmium toxicity. In the serum the smaller part of zinc is firmly bound to several specific proteins, the majority being loosely bound to albumin. Some aspects of human zinc metabolism in health and disease are reviewed. Zinc deficiency in man is rare. In Iran and Egypt a syndrome of iron and zinc deficiency associated with anaemia, hepatosplenomegaly, dwarfism, and hypogonadism is known. In wound healing and tissue repair substitution of zinc is beneficial only if a zinc deficiency exists. For purposes of long term parenteral nutrition zinc should be added to the different infusion solutions.