The discipline of behavioral toxicology is an acknowledgement that behavioral assessments should play a role in judging the safety of chemicals. Such a role is emphasized by the toxicological history of many different classes of substances. These include metals, insecticides, volatile organic solvents, and even food additives. For all of these, incipient toxicity often takes the form of subjective complaints that are later followed by overt impairments. The fetus and young child seem to be at special risk for substances such as methylmercury and synthetic food colors, a susceptibility not fully recognized.