A hazard index is an overall indicator of the potential harm of a hazardous substance to humans and the environment. This paper describes the use of a carcinogenicity index and a systemic (chronic) toxicity index in setting reportable quantities under Section 101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980. The three types of evidence used to evaluate a substance's carcinogenic hazard are (1) epidemiological, (2) experimental and (3) supportive evidence from short-term tests, metabolism and pharmacokinetics and structure-activity correlations. Hazardous substances suspected of carcinogenic potential are ranked by the level of this evidence and the potency factor. The potency factor is /ED(sub 10), where ED(sub 10) is the estimated dose associated with a lifetime cancer risk of 10%. The toxicity index for substances with systemic (chronic) toxicity potential is based on the minimum effective dose levels for chronic exposures via environmental media and the type of effect. About 200 potential carcinogens and 200 chemicals associated with other diseases have been evaluated and assigned a hazard ranking.