Between 60,000 and 100,000 of the over 8,000,000 chemicals listed by the Chemical Abstracts Services Registry are commercially produced and are potential environmental pollutants. Some kind of risk-based evaluation for these chemicals is often required to evaluate the impacts of chemical use or releases, for regulatory action, and to set priorities for pollution prevention. The time and resources, however, are not reasonably available to test all of these chemicals for their potential health and environmental effects. During the last decade there have been vast improvements in the methods used to test chemicals for toxicity and environmental fate and to interpret these data within a risk assessment framework. We have not, however, developed generally accepted and widely used tools to better enable us to set priorities and focus limited resources on selecting those chemicals for study that would yield the greatest environmental benefits. Risk-based ranking and scoring systems can be used to focus attention and resources on the largest potential hazards. Risk-based chemical ranking and scoring combines an assessment of both the toxic effects of chemicals (human and/or environmental) and the potential exposure to those chemicals to provide a relative evaluation of risk. Along with toxicity and exposure, ranking and scoring systems may include other environmental impacts (e.g. ozone depletion) and some measure of economic impact and/or societal value.