Although severe zinc deficiency has been previously induced in rhesus monkeys, marginal zinc deprivation, a state more analogous to that found in human populations has not been characterized. To address this issue, zinc deficiency was induced in mature female rhesus monkeys by restriction of dietary zinc in a semipurified diet based on sprayed egg white as the protein source. Groups of monkeys were fed dietary levels of 0.5, 2, 4, 8, 12, 20, or 100 ppm zinc. Plasma zinc concentration fell from an initial level of 92-148 μg/100 ml to levels between 40 and 90 μg/100 ml in monkeys fed 8 ppm zinc or less. This reduction in plasma zinc concentration was associated with alterations in peripheral blood lymphocyte mitogen responsiveness, taste sensitivity, and behavior similar to those seen in human zinc deficiency. However, in contrast to studies of severe zinc deprivation, our animals did not manifest alopecia, dermatitis, anorexia, or weight loss. It was concluded that marginal dietary zinc deficiency can be readily produced in primates and that depressed zinc levels achieved by this selective dietary restriction can lead to quantitative physiological changes without overt pathology. These findings are important for the development of a relevant animal model of marginal zinc deficiency.