1. Glomerular filtration rate, renal and systemic haemodynamics and intravascular volume were measured in 20 established essential hypertensive patients classified according to serum uric acid level into two groups (below 0.36 mmol/l, and above 0.54 mmol/l).
2. Although glomerular filtration rate was comparable between the two groups, renal blood flow was lower and renal vascular and total peripheral resistances were higher in the patients with the highest uric acid levels (P<0.02).
3. Cardiac output, heart rate and splanchnic blood flow were similar in both patient groups but arterial pressure tended to be higher in patients with high uric acid levels.
4. These data suggest that unexplained hyperuricaemia in patients with essential hypertension most likely reflects early renal vascular involvement, i.e. nephrosclerosis.