The author looks at the sharp increase in a number of childhood disorders--including asthma, certain cancers, and learning/behavioral disabilities--and the role environmental toxins may play in this increase. He describes the need to train many more health professionals in prenatal and children's environmental health and the national network of Pediatric Environmental Health Specialty Units that have been set up to help accomplish this. The article also describes the new National Children's Study, a multiyear prospective epidemiological study that will examine how early exposures to environmental factors influence health, disease, and development in children.