Much of the initial interest in the control of pollutants, both in the United States and abroad, focused on such 'traditional' pollutants as sulfur dioxide, particulate matter, Total Suspended Particulate (TSP) and particulate matter, nitrogen oxides, carbon monoxide, ozone, and lead. While there is still substantial room for progress in the control of some of the criteria pollutants, substantial progress has been made in understanding the impact of these pollutants and in regulating most of them. At the same time, another new group of pollutants has come to the forefront of the scientific and regulatory community. These non-criteria pollutants include organic compounds such as chlorinated organics, dioxins, aldehydes, and polycyclic organic compounds, as well as heavy metals such as cadmium and mercury. For many of the uncommon noncriteria pollutants, relatively little is known about their effects on health and the environment, and many of the potential effects could take decades to emerge. Similarly, ambient air emissions of many of these substances have not been systematically regulated in the past. Because most of the elevated exposures to these chemicals were thought to occur only in the workplace, widely divergent controls and regulations were enacted. Now that one realizes the pervasiveness of these pollutants in the ambient environment, they are grappling with ways to assess safe exposure levels to them. Cadmium is presented as an example of a standard-setting approach used to regulate noncriteria pollutants.