Nutrition exerts profound influence on immunological functions effecting both cell-mediated (humoral) and T cell-mediated (cellular) immune functions. Even the interaction of the immune systems can be profoundly influenced by restrictions or excesses of dietary constituents. In experimental systems where it is possible to control precisely the influence of specific nutriments, development and expression of autoimmune diseases and the associated immunodeficiencies of aging can be delayed by restrictions of dietary protein, protein and calories, fat, zinc, or even essential fatty acids. Tumor immunities likewise can be affected and sometimes even enhanced by restriction of protein, calories, or protein and calories, an influence associated with major delay in development of the experimental cancers--e.g. breast cancer. T cell-mediated immunodeficiencies associated with clinically apparent protein or protein calorie malnutrition are often attributable not to the major nutriment deficiencies per se but to accompanying zinc deficiency, a finding reflecting the vital role of zinc in many immunological functions. Dietary zinc deficiency appears to be responsible, at least in part, for the immunodeficiency that is so regularly associated with certain human cancers, such as epidermoid cancers of the head and neck region.