Bioassays are like safety drills for xenobiotics in the laboratory arena. Accordingly, they are conducted to measure or evaluate the toxicity or effects of known or suspected pollutants on species of test organisms. Their end-result can thus be used to set permissible discharge levels or rates, establish the relative sensitivity of various species of organisms, and identify effects of physical and chemical variables on the ecosystem biotopes. The methods used vary according to xenobiotic, organism, and environmental segment, among others.