Broadly defined as the scientific activity of evaluating the toxic properties of a chemical and the conditions of human exposure to it, with the objective of determining the probability that exposed humans will beadversely affected. Its four main components are: 1. Hazard Identification -- Does the agent cause the effect? 2. Dose-Response Assessment -- What is the relationship between the dose and its incidence in human beings? 3. Exposure Assessment -- What exposures are experienced or anticipated, and under what conditions? 4. Risk Characterization - The total analysis producing an estimate of the incidence of the adverse effect in a given population.