Atherosclerotic renal artery stenosis reduces blood flow and perfusion pressures to the poststenotic kidney producing renovascular hypertension and threatening glomerular filtration rate. Little is known regarding regional tissue oxygenation in human renovascular disease that develops slowly. We compared stenotic and contralateral kidneys regarding volume, tissue perfusion, blood flow measured by multidetector computed tomography, and blood oxygen level-dependent magnetic resonance values in the cortex and medulla in 14 patients with unilateral stenosis (mean: 71% by quantitative computed tomography) and in 14 essential hypertensive patients during 150 mEq/d of sodium intake and renin-angiotensin blockade. Stenotic kidney volume was reduced compared with the contralateral kidney (118.6+/-9.9 versus 155.4+/-13.7 mL; P<0.01), as was total blood flow (269.7+/-42.2 versus 383.7+/-49; P=0.02), mainly because of reduced cortical volume. Tissue perfusion was similar but lower than essential hypertension (1.5 versus 1.2 mL/min per milliliter; P<0.05). Blood oxygen level-dependent MR at 3 T confirmed elevated R2* values (a measure of deoxyhemoglobin) in deep medullary regions in all 3 sets of kidneys (38.9+/-0.7 versus cortex 17.8+/-0.36 s(-1); P<0.0001). Despite reduced blood flow, R2* values did not differ between atherosclerotic and essential hypertensive kidneys, although furosemide-suppressible fall in medullary R2* was reduced in stenotic kidneys (5.7+/-1.8 versus 9.4+/-1.9 s(-1); P<0.05). Renal venous oxygen levels from the stenotic kidney were higher than those from essential hypertensives (65.1+/-2.2 versus 58.1+/-1.2; P=0.006). These data indicate that, although stenosis reduced blood flow and volume, cortical and medullary oxygenation was preserved under these conditions.