The skeleton can play a unique role in modulating and responding to environmental air pollutants. Bone and its metabolic activities may be immediate targets for particular agents, leading to skeletal disease. However, bone is also an important storage site in the body. Chemical pollutants may be actively absorbed into bone mineral and released later during the normal process of bone remodeling. Critical periods when bone remodeling is enhanced, such as pregnancy, lactation, menopause, immobilization, and exposure to microgravity, may be important to recognize because of the potential for enhanced release of previously stored chemical agents. Lead has been identified as a "criteria air pollutant" by the 1970 Clean Air Act because of its ubiquity in the environment and its effect on a multiplicity of health outcomes. It is used in this article as an example of a substance that can have both a direct effect on bone and a latent effect on other organ systems through release from bone long after the initial exposure.