In 1986, the U.S. Environmental Protection Agency issued five guidelines for conducting risk assessments. The authors describe the process used by EPA to evaluate the health effects of exposure to environmental toxicants. When those guidelines were issued, EPA stated its intent to continue the development of new guidelines and revision of existing guidelines. The paper discusses the seven guideline activities under way as of September 1988: female reproductive risk, male reproductive risk, exposure measurements, developmental toxicity, carcinogenicity, non-cancer health effects, and neurotoxicity.