Summary. Immunohistochemical localization of 3β-hydroxysteroid dehydrogenase (3β-HSD) was performed in 55 cases of morphologically normal human ovaries by using a specific polyclonal antibody against purified human placental 3β-HSD. In small developing follicles, immunoreactivity was observed only in the theca interna but also became recognizable in the membrana granulosa with development of the follicle. At a late stage of folliculogenesis, the intensity of the 3β-HSD activity in the membrana granulosa was nearly equal to that of theca interna in 2 or 3 large follicles examined. One to several layers of theca interna cells just beneath membrana granulosa did not demonstrate any immunoreactivity of 3β-HSD or that of cytochrome P-450 17α-hydroxylase. These unstained theca interna cells did not appear to be directly involved in ovarian steroidogenesis and might be designated as 'enzymically inactive theca interna cells'. Marked immunoreactivity was observed in luteinized theca and granulosa cells of the corpus luteum.

Keywords: immunohistochemistry; human ovary; 3β-hydroxysteroid dehydrogenase; steroidogenesis