This paper discusses the evolving interdependent relationship between environmental sciences (such as epidemiology) and environmental law and regulation. Societal needs for expert evaluations of the potential hazards of toxic chemicals have tremendously influenced the development of toxicology and epidemiology. In this regard, much recent environmental law reflects its "shotgun wedding" with environmental science; these science-forcing laws require that regulatory agencies take action based on findings that may be at or, very often beyond, the frontiers of environmental science. Recent developments in environmental law and the growth of the animal protection movement have independently contributed to renewed interest in and heightened expectations for the role of epidemiology in developing environmental standards and actions. Those who oppose animal experimentation often argue that data on humans are required to estimate human effects; some recent laws, such as Superfund, mandate consideration of human health assessments as one of the bases for deciding whether and how best to clean up abandoned hazardous waste sites. Requiring epidemiologic confirmation of hazards would make evidence of human harm a prerequisite for regulatory action. Because the animal models and statistical tests on which much environmental regulation now rests are models designed to anticipate human and environmental effects, their statistical validation and development remain crucial to the development and application of environmental law. For the most part, epidemiology is best suited for confirming past risks and not for predicting and preventing future risks.