We measured glomerular filtration rate, renal and systemic hemodynamics, and intravascular volume in normotensive subjects and in borderline and established essential hypertensive patients classified according to serum uric acid level. Renal blood flow was lower and renal vascular and total peripheral resistances were increased in patients with high uric acid levels (p < 0.02). Serum uric acid concentration correlated inversely with renal blood flow/m2 body surface area (r = -0.45, p < 0.001) and directly with renal vascular (r = 0.41, p < 0.001) and total (r = 0.38, p < 0.001) resistance. Cardiac output, heart rate, and intravascular volume as well as glomerular filtration rate showed no uric-acid-department pattern. Mild asymptomatic hyperuricemia, therefore, was associated with decreased renal blood flow without affecting glomerular filtration rate. Increased renal vascular and total peripheral resistances reflecting renal and systemic hypertensive vascular disease paralleled the rising serum uric acid levels. These data suggest that heretofore unexplained hyperuricemia in patients with essential hypertension most likely reflects early renal vascular involvement, specially, nephrosclerosis.