The twentieth century has seen a remarkable evolution of environmental health and environmental protection concerns and concepts in the United States. As a teacher of Environmental Health since the late 1950s, I have witnessed the many twists and turns that have marked the latter half of the century, and have had to seek continuously to explain these phenomena to my students in some rational manner. We have witnessed the following and more: great progress in controlling acute infectious diseases through successes in drinking water treatment and food processing; the emergence of greater concern with trace chemicals in air and water and their role in chronic disease causation; conflicting attitudes toward miraculous chemicals such as DDT (which promised relief from arthropod-borne scourges, then came to be seen as another chemical threat to our children and our environment); then the reemerging concern with infectious diseases precipitated by blood-borne pathogens such as HIV. All this occurred against a backdrop of scientific uncertainty and amid failures of risk assessment and risk communication, together with press sensationalism-from mad cow disease to flesh eating streptococci. No wonder the public is confused.