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Bioassay (commonly used shorthand for biological assay), or biological standardisation is a type of scientific experiment. Bioassays are typically conducted to measure the effects of a substance on a living organism and are essential in the development of new drugs and in monitoring environmental pollutants. Both are procedures by which the potency (pharmacology) or the nature of a substance is estimated by studying its effects on living matter.



Bioassays are procedures that can determine the concentration of purity or biological activity of a substance such as vitamin, hormone, and plant growth factor. While measuring the effect on an organism, tissue cells, enzymes or the receptor is preparing to be compared to a standard precipitation. Bioassays may be qualitative or quantitative. Qualitative bioassays are used for assessing the physical effects of a substance that may not be quantified, such as abnormal development or deformity. An example of a qualitative bioassay includes Arnold Adolph Berthold's famous experiment on castrated chickens. This analysis found that by removing the testes of a chicken, it would not develop into a rooster because the endocrine signals necessary for this process were not available. Quantitative bioassays involve estimation of the concentration or potency of a substance by measurement of the biological response that it produces. Quantitative bioassays are typically analyzed using the methods of biostatistics.


"The determination of the relative strength of a substance (as a drug) by comparing its effect on a test organism with that of a standard preparation."



Bioassays are of two types:


A quantal assay involves an "all or none response". For example: Insulin induced hypoglycemic convulsive reaction or the cardiac arrest caused by digitalis. The response is either +ve or -ve , there is no intermediate response e.g.—either convulsion occurs or doesn't occur; similarly is with cardiac arrest.

In case of toxicity studies, the animal receiving a dose of drug either dies or dose not die. Here also no intermediate response is possible. This is also known as the "all or none" response assay. The quantal method though not accurate is employed for bioassay of substance in the following ways:
(a) Comparison of threshold response or
(b) Comparison of effective dose (ED50) or median lethal dose (LD50)

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