The sympathetic nervous system involvement in the pathogenesis of human renovascular hypertension was studied in 10 hypertensive patients with unilateral renal artery stenosis, who underwent percutaneous transluminal angioplasty (PTA). Before PTA, systolic/diastolic BP readings were 185.3 +/- 7.8/123.2 +/- 5.1 mmHg, peripheral PRA values were 8.63 +/- 2.27 ngAl/ml/h, the ratio RVRR was 2.15 +/- 0.27, the ratio V1-IVC/IVC was 1.00 +/- 0.23 (V1 = PRA from the renal vein of the stenotic side, IVC = PRA from the inferior vena cava) and the ratio V2-IVC/IVC was 0.04 +/- 0.02 (V2 = PRA from the renal vein of the non-stenotic side); 30 min after successful PTA the respective values of the above measured parameters were: 144.2 +/- 6.7/98.2 +/- 3.1 mmHg (p less than 0.01), 8.13 +/- 2.21 ngAl/ml/h (p less than 0.005), 1.79 +/- 0.19 (p less than 0.01), 0.68 +/- 0.18 (p less than 0.001) and 0.06 +/- 0.02 (p less than 0.005). Peripheral plasma noradrenaline levels (plNA) were 0.694 +/- 0.058 ng/ml, plNA levels from the renal vein of the stenotic side were 0.962 +/- 0.108 ng/ml and plNA levels from the renal vein of the non-stenotic side were 0.759 +/- 0.092 ng/ml; 30 min after successful PTA the respective values were 0.518 +/- 0.055 ng/ml (p less than 0.01), 0.681 +/- 0.078 ng/ml (p less than 0.005) and 0.510 +/- 0.063 ng/ml (p less than 0.005). It is suggested that the reversal of chronic renal ischaemia by PTA induced statistically significant changes in the sympathetic nervous system activity, parallel to the changes of renin secretion.