We have shown that relatively insoluble salts of zinc can be suspended in a benzylbenzoate caster oil vehicle and injected into rats or monkeys from once weekly to once monthly with marked elevation of plasma levels of zinc. The relative water solubility of the zinc salts, at least over the two orders of magnitude of solubility ranges studied, seems not to influence the plasma zinc response. However, a dose-response relationship ocurs: the more zinc injected per unit time, the higher the plasma zinc concentrations. In the monkey, the sensitivity of the plasma zinc response increases by approximately one order of magnitude compared to that of the rat, when based upon the dose of zinc injected per kilogram of body weight. This depot method offers advantages over other methods for animal studies of zinc. It may eventually find therapeutic application in man as well.