The aim of these examinations was to determine the influence of dexamethasone (Dx)-treatment of gravid females, on day 16 of gestation on the development of medullary chromaffin tissue of their fetuses and neonatal offspring. In conducting these investigations we used stereological as well as spectrofluorimetric measurements, in 20-day-old fetuses and 1-, 3-, 5-, 7-, 9-, 11-, 13- and 14-day-old neonatal rats. Single Dx-treatment (1.5 mg/kg bw) of the dams led to a significant decrease in body and adrenal weight of their fetuses and neonatal offspring, and also reduction of the medullary volume and the number of chromaffin cells during the entire period examined as a result of decreased cell proliferation in the fetal and early neonatal period (till the 5th day of age). The proliferative activity of the chromaffin cells was evaluated through the mitotic index after applying the cytostatic vincristine-sulphate. During the second neonatal week the mitotic index showed significantly higher values in comparison with the corresponding controls, which indicates that there is regeneration and recovery of the adrenal gland medulla. Adrenaline content in the adrenal gland tissue of offspring of Dx-treated dams was significantly reduced only on the 1st neonatal day. Thus, the change in blood glucocorticoid level of pregnant females after a single Dx injection during the period critical for development of the hypothalamo-pituitary-adrenal system in fetuses affects the development and kinetics of medullar chromaffin cell division.