The evaluation of patients with inadequate control of diastolic blood pressure for surgically correctable forms of hypertension led to the detection and surgical treatment of 56 patients. Detection was facilitated by the use of hypertensive intravenous pyelography and Hippuran renal Scanning. Aortography proved the presence of renal artery disease and renal vein renin assay established its significance in the etiology of the patients' hypertension. Renal artery reconstruction was performed in 50 patients, including 5 who also had reconstruction of major aortoiliac lesions. The extent of renal artery disease precluded arterial reconstruction in six patients, who required nephrectomy. Two postoperative deaths occurred, for a mortality rate of 3.6 per cent. Improvement in mean diastolic blood pressure for the total group of patients from 118 mm Hg preoperatively to 86 mm Hg postoperatively was achieved. Forty-six patients (85 per cent) have a diastolic blood pressure of 90 mm Hg or less; in 5 patients the diastolic blood pressure is 91 to 100 mm Hg but is at least 20 mm Hg lower than the preorative level.