An unidentified teratogen, as detrimental to fetal development as thalidomide, may lurk in our environment. That news comes from investigators who are now seeing infants born (in places as diverse as Alaska and Florida) with imperforate anus, renal agenesis or dysplasia, postaxial polydactyly, nail dysplasia, unusual facies, multiple frenula of the gums, laryngeal clefts, bifid or absent epiglottis, and additional anomalies that vary from case to case. The affected infant invariably dies shortly after birth. Autopsy reveals a bizarre hypothalamic tumor that has resulted in a malformed pituitary area. The resulting absence of functional pituitary tissue accounts for the hypopituitarism, hypoadrenalism, and, in males, microphallus that also characterize the syndrome. In four of six known cases, says Judith Hall, MD, the mothers reported exposure to herbicides or pesticides (including an unidentified substance sprayed on plants at a campsite and a common commercial fumigant for household use) early in the first