The following is the fifth in our series of review articles on the developmental biology of the nervous system and its relation to diseases and disorders that are found in newborn infants and children. In this article Drs. Edwards Infants are subjected to both endogenous and exogenous corticosteroids in the pre-and postnatal periods. Stress to the mother before birth, or to the child postpartum, can give rise to high, chronic endogenous corticosteroid levels caused by activation of the hypothalamic-pituitary-adrenal (HPA) axis. Physician-administered exogenous corticosteroids are also used in the management of a wide spectrum of pre-and postnatal conditions. The long-term effects of corticosteroids in developing humans are not well known. Studies in animals, however, indicate that both natural stress and exogenous corticosteroids can have longlasting and deleterious effects on the body, brain, behavior, and hypothalamic-pituitary-adrenal axis of developing infants. These data suggest that exogenous corticosteroids should be administered with caution, after careful benefit/risk analyses, and that, as far as possible, the developing brain should be protected against the effects of pre-and postnatal stress. Abbreviations: HPA, hypothalamic-pituitary-adrenal axis PVN, paraventricular nucleus CRH, corticotropin-releasing hormone POMC, proopiomelanocortin GR, glucocorticoid receptor MR, mineralocorticoid receptors GABA, gamma amino butyric acid MHC, major histocompatibility complex 11-HSD, 11-hydroxysteroid dehydrogenase Infants are subjected to both endogenous and exogenous corticosteroids in the pre-and postnatal periods. When pregnant women undergo prolonged stress, for instance, such as that caused by family discord or the death of a spouse, the unborn infant is subjected to high, chronic levels of endogenous corticosteroids (1, 2). This is a result of repeated activation of the mother's HPA axis (1). Postnatally, traumatic events in the child's life give rise to high, chronic corticosteroid levels, resulting from activation of the child's own HPA axis (3).Exogenous glucocorticoids are also used in the management of a wide spectrum of pediatric diseases. Prenatally-and in