ALTHOUGH several procedures have been recommended for the detection of patients suffering from correctable renal hypertension, none has proved to be adequate for the purpose, and the decision to undertake surgical intervention is based frequently on an educated guess. Stenosis of the renal artery remains the most commonly accepted indication of the possible presence of surgically remediable hypertension.^1-13 However, this lesion is encountered frequently in normotensive patients¹⁴ and its repair is often not followed by reduction of the elevated blood pressure. Another commonly used diagnostic procedure for detecting correctable renal hypertension utilizes the decreased volume and sodium content of the urine of the affected kidney, as described first by Connor et al ^1,2 and modified by Dustan et al,³ Stamey et al,¹³ Rapaport,¹⁵ Birchall et al,¹⁶ and others. This procedure likewise has failed to provide a decisive method for detecting patients with unilateral renal disease. The histological appearance of the