(a) A relationship in which a change in amount, intensity duration of exposure is associated with a change-either an increase or a decrease-in risk of a specified outcome. [Last, 1983: A Dictionary of Epidemiology]; (b) The relationship between the dose of a vaccine and an immune or physiologic response. In vaccine research, a dose_response effect means that as the dose of the vaccine increases, so does the level of the immune response (antibodies and CTL activity). [NIAID, 1997: HIV Vaccine Glossary]; (c) The resulting biological responses in an organ or organism expressed as a function of a series of different doses. [USEPA, 1992: GL for Exposure Assessment] [USEPA, 1997b: Exposure Factors Handbook]; (d) A relationship between (1) the dose, either "administered dose" (i.e., exposure) or absorbed dose, and (2) the extent of toxic injury produced by that chemical. Response can be expressed either as the severity of injury or proportion of exposed subjects affected. A dose_response assessment is one of the four steps in a risk assessment. [USEPA, 1995: Benchmark Dose]; (e) The quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease produced. [USEPA, 1997a: EPA Terms of Environment] [USDOE, 2000: RAIS Glossary]; (f) The relationship between a quantified exposure (dose), and the proportion of subjects demonstrating specific, biological changes (response). [IRIS, 1999: Glossary of IRIS Terms]