Chronic administration of dexamethasone in drinking water to maternal rats from days 15 to 21 of gestation (1) reduced plasma testosterone concentrations in male fetuses between days 19 and 21 but not earlier on day 18 and abolished the prenatal peak of plasma testosterone which normally occurs on day 19 of gestation, and (2) suppressed the postnatal surge of plasma testosterone in male newborns 1.5 and 2 h after delivery at term by cesarean section. The administration of dexamethasone to male fetuses at birth induced 1 h later a slight but not significant increase in hypothalamic gonadotropin-releasing hormone (GnRH) and pituitary luteinizing hormone (LH) contents, reduced drastically plasma LH levels and completely prevented the postnatal surge of plasma testosterone which occurred normally in littermate controls. A rise in pituitary LH content, and a sharp reduction in plasma LH and testosterone concentrations were noted in 19-day-old male fetuses whose mothers were acutely treated with dexamethasone on day 18 of gestation. Similar evolutions for LH were observed in littermate females. These results suggest that the inhibitory effects of exogenous glucocorticoids on testosterone secretion could be mediated in both fetuses and newborns at least partially through suppression of the hypothalamic and pituitary secretion of GnRH and LH, respectively, and provide insight how stress or hormone imbalance may affect the development of this neuroendocrine system.