Primary aldosteronism (PA) has been recognized as a common cause of secondary hypertension and accounts for approximately 5-15% of the hypertensive population in Japan. Screening for PA should therefore be carried out in all hypertensive patients as we have shown the estimated prevalence of PA is 13.6% in pre-hypertensive subjects and 9.1% in stage 1 hypertensive patients. The screening test most advocated is the aldosterone-to-renin ratio (ARR), and when the ARR is >20 the following confirmatory tests should be carried out; the captopril challenge test, frusemide-upright test, or saline infusion test. Adrenal CT is not accurate for distinguishing between an aldosterone-producing adenoma (APA) and idiopathic hyperaldosteronism (IHA). Adrenal venous sampling (AVS) is therefore essential for selecting the appropriate therapy in patients a high probability of PA who require surgical treatment. Rapid cortisol assays during AVS to monitor cortisol levels can reduce the failure associated with AVS. We have developed a new rapid cortisol assay using immunochromatography, in which cortisol concentration can be measured within 6 min. Using this technique, the success rate of AVS improved to 93%. IHA underlies about one-half of cases with PA; treatment with eplerenone (100 mg twice a daily), a specific mineralocorticoid receptor antagonist, results in substantial improvement in hypertension, with fewer side effects compared to spironolactone.