The enzyme aromatase (P450(AROM)) converts testosterone (T) into 17-beta estradiol (E-2) and is crucial for the control of development of the central nervous system during ontogenesis. The effects of E-2 in various brain areas are mediated by the estrogen receptor alpha (ER-alpha) and the estrogen receptor beta (ER-beta). During fetal development, steroids are responsible for the sexual differentiation of the hypothalamus. Estrogens are also able to exert effects in other brain areas of the fetus including the frontal cortex, where they act through estrogen receptors (ERs) modulating cognitive function and affective behaviors. In this study we have determined the expression profiles of P450(AROM) and ERs in the fetal bovine frontal cortex by quantitative Real-Time PCR (qRT-PCR) throughout the prenatal development. The data show that the patterns of expression of both ERs are strongly correlated during pregnancy and increase in the last stage of gestation. On the contrary, the expression of P450(AROM) has no correlation with ERs expression and is not developmentally regulated. Moreover, we performed immunochemical studies showing that fetal neurons express P450(AROM) and the ERs. P450(AROM) is localized in the cytoplasm and only seldom present in the fine extensions of the cells; ER-alpha is detected predominantly in the soma whereas ER-beta is only present in the nucleus of a few cells. This study provides new data on the development of the frontal cortex in a long gestation mammal with a large convoluted brain. (C) 2011 Elsevier Inc. All rights reserved.