As defined in Lecture 1 (Slide 10), risk is the likelihood or potential that an adverse outcome would occur. Thus, the discussion on the close relationship between RA and toxicology, or between RA and epidemiology, should start with the perceptions of risk and health (herein also health risk perception). It is these elements that affect the public’s choices of health programs and drive the movement of RA, the latter relying heavily upon the use of toxicity and exposure data. The impact of risk and health perceptions perhaps can be illustrated with the example given by Neely (1994). In the United States, roughly 20,000 to 30,000 deaths occur every year in traffic accidents caused by drunk driving. This statistic is accepted with little concern, especially in terms of prevention and regulatory action. Yet the great tampon-toxic shock scare of a decade ago received a great deal of public attention, despite the fact that the total number of victims did not amount to one weekend’s traffic fatalities. Meanwhile, a lot of research efforts is being made to understand AIDS, which ironically is a well preventable social disease.