Determination of the potency or concentration of a compound by its effect upon animals, isolated tissues, or microorganisms, as compared with an analysis of its chemical or physical properties: A bioassay is an experimental technique for measuring quantitatively the strength of a biologically active chemical by its results on a living organism.

A bioassay uses living organisms to measure the quantity and efficacy, especially of a toxic quality, of a substance, factor, or condition.

• The vitamin activity of certain substances can be measured using bacterial cultures.
• The increase in bacterial numbers is compared against that achieved with known standards for vitamins.
• Plant growth hormones can be estimated by their effect in causing curvature of oat coleoptiles (a sheathlike structure that protects the developing plumule [first rudimentary leaves in the mature embryo and seedling] in grasses).