We performed computed tomography (CT) in 22 consecutive patients with primary aldosteronism to evaluate the usefulness of this technique in diagnosing and locating aldosterone-producing adenomas. Sixteen patients had severe hypokalemia, hyperaldosteronism, and elevated plasma levels of 18-hydroxycorticosterone suggestive of an adenoma. In 12 of these 16, a unilateral adrenal mass was demonstrated clearly, and in all 11 who had surgery in adenoma was confirmed. In the other four patients in this group, one adrenal gland was normal and the other was either not seen adequately or had minor abnormalities that could not be definitely classified; an adenoma was found in the poorly visualized gland in each of the two patients who had surgery. The remaining six patients, who had milder biochemical abnormalities suggestive of idiopathic hyperaldosteronism, had bilateral adrenal enlargement or normal-appearing glands on scan and were not surgically explored. We conclude that CT scans, together with appropriate biochemical measurements, are useful in diagnosing and locating aldosterone-producing adenomas.