Childhood exposure to chemicals routinely encountered in the environment has become an issue of scientific and public concern. Recent research has revealed the inadequacy of traditional notions in which chemically induced illness was likened to overt biological disease. The new multiple-effects model emphasizes subtle behavioral alteration as an early sign of toxicity and as evidence that a particular chemical agent may produce long-term impairment in susceptible individuals. Moreover, the permeability of the placenta to a variety of chemical agents and the special sensitivity of the fetus to some of these agents draws attention to prenatal exposure and the need for prospective longitudinal studies of affective, social, and cognitive development in exposed individuals. The multiple-effects model provides an important new role for the psychologist in teratological diagnosis and research since the measurement of behavioral variation has developed primarily in our discipline. Limitations inherent in both experimental animal research and correlational human studies of toxic effects make it necessary for these methodologies to be used in a complementary fashion. The implications of behavioral teratology for the study of human development and the design of protective social policies are also discussed. (Copyright (c) by the American Psychological Association, Inc. 1983.)