The aldosterone-to-renin ratio (ARR) is an accepted screening tool for primary hyperaldosteronism (PA). An ambulatory case finding test to separate surgically remediable aldosterone-producing adenoma (APA) from other forms of PA, however, is currently not available. The aim of this study was to evaluate a reverse postural test (RPT) as a novel tool for identifying APA. We investigated 6 healthy controls, 19 primary hypertensive patients, and a prospective cohort of 32 patients clinically suspicious for primary hyperaldosteronism. We diagnosed seven patients with surgically proven APA, and three patients with idiopathic hyperaldosteronism. Serum aldosterone was measured after 30-min of moderate exercise (Aldo-1) and after a subsequent 2-h supine resting period (Aldo-2) with calculation of the ratio Aldo-2/Aldo-1. Aldosterone significantly decreased after supine resting in both healthy controls and primary hypertensives, but not in patients with APA. Receiver-operating-curve analysis revealed that the RPT was suitable for the screening of APA. A combination of the ratio Aldo-2/Aldo-1 >0.59 and Aldo-2 >160 pg/ml correctly identified all the patients with APA, with no false positives. Although the high sensitivity of the RPT here observed needs to be confirmed in larger studies, the high positive predictive value of RPT could be useful for the identification of APA in outpatients.