Fetal exposure to cyproterone acetate (CPA), while allowing, normal sexual morphogenesis, has previously been shown to lead to functional endocrine abnormalities in adult rats of both sexes. Because of this, we examined morphologically and morphometrically the hypothalamic nuclei involved in sexual dimorphism as well as the pituitary lactotropes of rats exposed in utero from day 15 to 20 of gestation to CPA. Male and female offspring was studied at the age of 70-80 days. In both sexes the brain weight was lower (p less than 0.05) in CPA-treated than in control rats. Morphometrical investigations showed that the surface density (Sv) and the volume density (Vv) of the ventromedial nucleus were higher (p less than 0.05) in CPA-treated male than in control rats. By comparing sexes the Sv and Vv of the ventromedial nucleus were higher (p less than 0.01) in CPA-treated male than in corresponding female rats. Also the nuclear surface of the tyrosine hydroxylase-immunoreactive neurons of the arcuate nucleus was higher (p less than 0.05) in CPA-treated male than in female rats. In lactotropes of the pituitary gland the immunoreactive prolactin (PRL) was densitometrically increased (p less than 0.05) in CPA-treated female compared with control rats. By electron microscopy, PRL granules and autophagocytosis appeared to be more abundant in CPA-treated rats of both sexes. These data show that fetal exposure to CPA results in long-term anatomical and physiological alterations of hypothalamic and preoptic nuclei as well as of the pituitary lactotropes. These permanent changes support the functional endocrine abnormalities observed in adult rats.