The effect of synthetic glucocorticoid, dexamethasone (DEX), on the fine structure of the fetal growth hormone (GH) cell was examined in rats on Days 17-19 of gestation by the protein A-gold method of immuno-electron microscopy. GH cells appeared on Day 19 in the control fetuses. The DEX-induced GH cells of Day 17 fetuses displayed more immature features than those of Day 18, which closely resembled GH cells found in the control fetus on Day 19. Cytological changes which indicate increased secretory activity such as the development of the rough endoplasmic reticulum or enlargement of the Golgi complex, and an accumulation of secretory granules were evident only in the DEX-treated fetuses on Day 19. It is concluded that DEX not only accelerates the development of GH cells, as observed on Day 17 or 18, but also brings them to a functionally stimulated state by Day 19.