Angiotensin II (Ang II) AT1 receptors modulate most of the known physiological functions of Ang II in the kidney and cardiovascular structures. In contrast, the physiological role of AT2 receptors, which are abundantly expressed in fetal tissues, is not clearly defined. The changes that occur in the expression and distribution of AT2 receptors in the kidney and arteries during the first 2 years of life have not been studied. We have localized and characterized the expression of Ang II receptor subtypes, AT1 and AT2, in the kidney, interlobular arteries, thoracic aorta, and middle cerebral artery, in children during their first 2 years of life, using quantitative autoradiography. Renal glomeruli and middle cerebral arteries expressed exclusively AT1 receptors. In contrast, more than 80% of the Ang II receptors expressed in thoracic aorta and interlobular arteries belonged to the AT2 subtype. These findings demonstrate that the expression of Ang II receptor subtypes in different vascular structures in young children varies according to the tissue.