The paper was presented as the introduction to a session on the history and epidemiology of prenatal chemical exposure. Although teratology and developmental toxicology had its experimental beginnings in the early part of this century, the potential for human developmental toxicity due to chemical exposure was not generally recognized until the thalidomide tragedy of the early 1960s. Furthermore, the fact that exposure to chemicals during development might have subtle and long-lasting postnatal consequences in humans was not generally recognized until the late 1960s and early 1970s. The data available are usually most extensive for therapeutic agents or environmental chemicals for which standard testing is required prior to marketing or release into the environment. For substances of abuse, on the other hand, there is no standard testing unless the drug is a therapeutic agent, and data may be sketchy or nonexistent until a problem is recognized in humans. It is important to educate the general public about the drastic consequences of drug abuse during pregnancy.