In situ hybridization studies have suggested that the subtype 2 angiotensin (AT₂) receptor gene is expressed in fetal and newborn rat kidney but is undetectable in the adult animals. In the present study, we investigated the expression of AT₂ receptor protein in the fetal (days 14 and 19 of fetal life), newborn (day 1 postpartum), and adult (4-week-old and 3-month-old) rat kidney. Polyclonal anti-peptide antiserum was raised against the amino terminus of the native AT₂ receptor. The selectivity of the antiserum was validated by recognition of the AT₂ receptor in a stably transfected COS-7 cell line by Western blot and immunocytochemical analysis. As a positive control, the AT₂ receptor signal was detected strongly in the adrenal gland. Positive immunohistochemical staining was observed in the mesenchymal cells and ureteric buds of the 14-day fetal kidney and in the glomeruli, tubules, and vessels in the 19-day fetal and newborn kidney. Glomeruli expressing the AT₂ receptor were localized mainly in the outer layer of the renal cortex. In the young (4-week-old) and mature (3-month-old) adult rat on normal sodium intake, renal AT₂ receptor immunoreactivity was present in glomeruli but substantially diminished compared with that of newborn rats. In both young and mature adult rats, dietary sodium depletion increased the renal AT₂ receptor signal, mainly in the glomeruli and interstitial cells. Preimmune and preadsorption controls were negative. Western blot analysis detected a single 44-kD band in the fetal and newborn rat kidney and in the young and mature adult rat kidney. Dietary sodium depletion increased the density of the AT₂ receptor band in mature adult rat kidneys. These data provide evidence that the AT₂ receptor protein is expressed in the fetal and newborn rat kidney, diminishes in adult life, and is reexpressed in the adult in response to sodium depletion.