Quantitative autoradiography was used to characterize angiotensin AT₁ and AT₂ receptors, in the rat aorta at three developmental ages; embryonic day 18 (E18), and postnatal weeks 2 and 8. The expression of angiotensin receptors was higher in the aorta of E18 and 2-week-old rat. A major proportion of the angiotensin receptors expressed in the aorta at these two ages was AT₂ (84 and 81% respectively). Conversely, in the aorta of 8-week-old rats, AT₁ was the predominant angiotensin receptor subtype (71%). In 8-week-old rats, the AT₂ subtype was also present (28%). In pre- and postnatal rats, [¹²⁵I]Sar¹-angiotensin II binding to AT₁ receptors was sensitive to GTPγS whereas binding to AT₂ receptors was not. AT₂ receptors may serve an important role during stages of rapid growth of the aorta, and also have a significant function in the adult vasculature.