A bioassay is a quantitative test of the adverse or toxic effects of a chemical on a living organism. Toxic effects may include both lethality (mortality) and subacute effects such as changes in growth, development, reproduction, pharmacokinetic responses, pathology, biochemistry, physiology, and behavior. Effects are expressed by quantifiable criteria such as number of organisms killed, percent egg hatchability, changes in length and weight, percent enzyme inhibition, number of skeletal abnormalities, or tumor incidence.

When measuring the toxicity of a chemical in a bioassay, the objective is to estimate as precisely as possible the range of chemical doses or concentrations that produce some selected, readily observable, quantifiable results in groups of the same test species under controlled laboratory conditions. The results of the exposure are plotted on a graph that relates the dose or concentration of the test chemical to the percentage of organisms in test groups exhibiting the...