Zn deficiency can have marked effects on virtually all components of the immune system. That these effects can be functionally significant is demonstrated by the increased susceptibility of Zn-deficient animals to a number of bacterial, viral, and parasitic challenges. In addition, strong epidemiological data support the belief that Zn deficiency is a major factor underlying immune dysfunction in select human populations. Despite recognition of the importance of Zn in the ontogeny and functioning of the immune system, the biochemical lesions underlying the effects of Zn deficiency on immune responsivity have not been well characterized. Future efforts to delineate the effects of Zn on the production, release, and action of cytokines will likely produce significant advances in our understanding of the influence of this element on the immune system. The recent observation that Zn may be critical for the activity and binding of protein kinase C in lymphocyte membranes suggests that another fruitful area of research will involve examination of the influence of Zn deficiency on lymphocyte membrane structure and function. Finally, the recent recognition that Zn may be a critical factor in the activation/inactivation of immunoregulatory genes provides us with yet another avenue of research.