The effects of graded levels of dietary zinc on the development and mineralization of teeth and bones and on the susceptibility of teeth to dental caries were studied in young growing rats. Thirty-six weanling male Sprague-Dawley rats were randomly assigned to four dietary treatments: 1) zinc-deficient, less than 1 ppm; 2) 12 ppm zinc; 3) 36 ppm zinc, and 4) 108 ppm zinc. For treatments 2, 3 and 4, rats were pair-fed the quantity of feed consumed by their individual counterparts fed the zinc-deficient diet. After 4 weeks of treatment, growth retardation along with other clinical zinc deficiency signs were observed in rats fed the zinc-deficient diet. The zinc levels in bones and teeth of zinc-deficient rats were lower than those for rats fed supplemental zinc. Increased dietary zinc resulted in greater levels of zinc in bones and teeth, but the levels of calcium decreased. Greater incidences of enamel lesions in mandibular molars were observed in rats fed the zinc-deficient diet than in rats pair-fed zinc-supplemented diets. Furthermore, the effect of zinc deficiency on dental caries of young rats was predominantly at the smooth surfaces of the molars. Dietary zinc may be an important trace mineral in the process of post-eruptive mineralization of the enamel and may reduce the susceptibility of teeth to caries.