In the present study we investigated the ontogeny of the expression of the type 1 angiotensin receptor (AT₁R mRNA) and the zonal localization of AT₁R immunoreactivity (AT₁R-ir) and cytochrome P450_c11 (CYP11B-ir) in the sheep adrenal gland. In the adult sheep and in the fetus from as early as 90 days gestation, intense AT₁R-ir was observed predominantly in the zona glomerulosa and to a lesser extent in the zona fasciculata, and it was not detectable in the adrenal medulla. AT₁R mRNA decreased 4-fold between 105 days and 120 days, whereas AT₁R mRNA levels remained relatively constant between 120 days and the newborn period. In contrast, both in the adult sheep and in the fetal sheep from as early as 90 days gestation, intense CYP11B-ir was consistently detected throughout the adrenal cortex and in steroidogenic cells that surround the central adrenal vein. In conclusion, we speculate that the presence of AT₁R in the zona fasciculata, and the higher levels of expression of AT₁R at around 100 days gestation, may suggest that suppression of CYP17 is mediated via AT₁R at this time. The abundant expression of AT₁R-ir and CYP11B-ir in the zona glomerulosa of the fetal sheep adrenal gland would also suggest that lack of angiotensin II stimulation of aldosterone secretion is not due to an absence of AT₁R or CYP11B in the zona glomerulosa.