Hypothesis: Zinc deficiency is a major public health problem in developing counties. Poor zinc status is associated with stunted growth and reduced resistance to infections. Several in vitro experiments and in vivo studies in animals and humans have demonstrated detrimental effects of zinc depletion on almost all facets of the immune system. The epithelial linings in the gut and in the respiratory tract are important for the resistance to infections and continuous cell division is required for proper function of these barriers. Zinc is crucial for cellular division and for the maintenance of organs with cells with a rapid turnover, including epithelial cells. Clinical trials in children in developing countries have demonstrated improved growth and reduced prevalence of diarrhea and respiratory tract infections following zinc supplementation. Furthermore, zinc has a well-documented therapeutic effect when given during acute or persistent diarrhea. The effect of zinc may be explained by correction of a deficiency state and/or by a pharmacological, as yet poorly described, action.