Glucocorticoids and thyroid hormones control many aspects of fetal development. Using immunohistochemistry and stereology, in the present study we investigated the effects of dexamethasone (Dx) administration during pregnancy on pituitary TSH cells of 19-day-old fetuses. Doses of 1.0, 0.5, and 0.5 mg Dx/kg bw/day were given to the dams on three consecutive days starting on day 16 of gestation. Administration of Dx to pregnant rats induced a significant decline of fetal TSH cell number per unit of area and their volume density in comparison with the corresponding controls. Our results showed that maternal Dx administration inhibited multiplication of TSH cells in 19-day-old fetuses.