The aim of this investigation was to examine the interrelation between renal mRNA levels of renin and angiotensin II receptor type 1 (AT₁) in a renin-dependent form of experimental hypertension. Rats were studied 4 weeks after unilateral renal artery clipping. Mean blood pressure and plasma renin activity were significantly higher in the hypertensive rats (n=10 206±8 mm Hg and 72.4±20.9 ng · mL⁻¹ · h⁻¹, respectively) than in sham-operated controls (n=10, 136±3 mm Hg and 3.3±0.5 ng · mL⁻¹ · h⁻¹, respectively). Northern blot analysis of polyA⁺ RNA obtained from the kidneys of renal hypertensive rats showed increased levels of renin mRNA in the clipped kidney, whereas a decrease was observed in the unclipped kidney. Plasma renin activity was directly correlated with renin mRNA expression of the poststenotic kidney (r=.94, P<.01). AT₁ mRNA expression was lower in both kidneys of the hypertensive rats. This downregulation was specific for the AT_1A subtype since the renal expression of the AT_1B subtype remained normal in hypertensive rats. The downregulation of the renal AT_1A receptor may be due to high circulating angiotensin II levels. This is supported by the significant inverse correlation (r=−.71, P<.01) between plasma renin activity and AT_1A mRNA expression measured in the clipped kidney of the hypertensive rats.