New diagnostic techniques have enhanced the detection of primary aldosteronism. However, the response of blood pressure after operation in unilateral and bilateral adrenal disease is different. We have compared four localizing techniques—adrenal venography, adrenal isotopic scanning, a modified adrenal venous sampling for steroid measurements, and the anomalous postural decrease in plasma aldosterone concentration—in 51 patients with primary aldosteronism, all of whom had undergone operative confirmation. Adrenalectomy resulted in normal blood pressure in 59%, improvement in 25%, and no change in 16%. Correct localization of the lesion was obtained in 47% by the adrenal isotopic scan, in 66% by adrenal venography, and in 91% by the modified adrenal venous hormone technique despite four false-positives. Of the 26 patients with an anomalous postural decrease in plasma aldosterone, 88% had a unilateral lesion.