A retrospective analysis of peripheral and renal vein plasma renin activity has been performed in 9 patients with bilateral renal artery stenosis (3 fibromuscular dysplasia and 7 atherosclerosis). In all cases angiography showed a reduction of the arterial diameter of more than 70 p. 100. The renal artery was occluded in 3 cases. All patients received a constant sodium diet (100 mEq/day). Peripheral PRA values were classified as normal or low in 6 cases (less than 2.8 ng/ml/h) and high in one case (greater than 2.8 ng/ml/h): this values concerned 2 cases with renal artery occlusion and 1 case with a narrowing of 90 p. 100. Renal venous renin ratio of 1.5 or more has been found in 8 cases. In one case, the stenosis was quite symmetrical (70 p. 100) and the ratio less than 1.5. The secretion index has been calculated as the ratio between the venoarterial difference of both affected and unaffected side over the arterial value of PRA (V-A/A). On the more stenosed side, was found a V-A/A ratio of 0.5 or more. This ratio is particularly high in case of artery thrombosis, but there is no correlation between the ratio and the degree of stenosis. On the contralateral side, where the lesions were less important, the V-A/A ratio was low, ranging from 0 to 0.2; this estimation of renin secretion was found despite a significant stenosis on the angiography. 7 patients underwent PTA or surgery. 2 kidneys with arterial thrombosis were nephrectomized. In 5 cases the surgical treatment is performed on the 2 sides during the same procedure.(ABSTRACT TRUNCATED AT 250 WORDS)