Epidemiology and risk assessment have several of the features needed to make the difficult decisions required in setting standards for levels of toxic agents in the workplace and environment. They differ in their aims, orientation, and time scale. While the distribution of disease provides the focus for epidemiologic research, concern for adverse effects of specific toxicants drives risk assessment. Most important, while epidemiology is a scientific field that draws upon medicine, demography, and statistics, risk assessment is a hybrid of science and policy that draws not only upon fields such as epidemiology, toxicology, chemistry and engineering, but also upon psychology, politics, economics, law and social justice. These inherent differences in emphasis, timing, and nature complicate the role played by epidemiology in risk assessment for regulatory policy. It will continue to play an essential part in regulatory decision-making. The role has placed epidemiologic findings and epidemiologists at the center of political controversies, with both positive and negative side effects of this new visibility. Ways to prevent the negative side effects and ways to increase the utility of epidemiologic data for regulatory risk assessment are explored. (Copyright (c) 1986 Pergamom Journals, Ltd.)