The thalidomide tragedy which occurred slightly more than a decade ago made public officials and the general public acutely aware of the teratogenic potential of drugs. Although specialists in pharmacology and developmental biology had been studying this problem many years before, this catastrophic episode triggered the passage of legislation which required that information about the teratogenicity of drugs be produced before the drugs could be available to the general public. Gross deformities in man produced by drugs are frequently difficult to reproduce in experimental animals and the changes which are produced in other animals are frequently not translatable to humans. The problem of evaluating the potential that drugs have to produce gross malformations is small, however, compared to the evaluation of subtle but permanent behavioral effects which drugs may exert upon the developing organism. Nevertheless, many experimental studies in recent years indicate that subtle biochemical changes produced by drugs on brain tissue during critical periods of fetal or early post natal maturation may become manifest subsequently as behavioral deviations in early childhood or adolescence. Hyperkinetic disorders, epilepsies and other developmental disabilities may have a subtle biochemical imbalance, perhaps drug induced, as an underlying factor. This symposium was organized with the intent of bringing to gether prominent investigators who are working in different aspects of brain development and who are interested in the effects of drugs on the developing brain in order to discuss their findings, pro pose new theories, and open new avenues for future research.