The smallest quantity of a pathogenic agent or concentration of a substance that is capable of producing a measurable outcome, such as occurrence of disease or relief of symptoms. Applied to ionizing radiation such as x-rays, it is an exposure level adequate for diagnostic purposes but insufficient to have harmful consequences. When long-term followup studies revealed adverse effects of even small exposures to diagnostic x-rays, this dose was revised downward. In toxicology, ED50 is the dose that has a measurable effect on 50% of subjects. Compare ld50.
Subjects: Public Health and Epidemiology.