a steroid hormone secreted by the adrenal gland. It serves as the principal regulator of the salt and water balance of the body (a mineralocorticoid) and has a small effect on the metabolism of fats, carbohydrates, and proteins.

Aldosterone is synthesized in the body from corticosterone, a steroid derived from cholesterol. Production of aldosterone (in adult humans, about 20–200 micrograms per day) in the zona glomerulosa of the adrenal cortex is apparently regulated by renin angiotensin secreted from the kidney in response to variations in blood pressure and volume, and plasma sodium and potassium levels. It influences salt and water retention by an effect on the proximal tubules of the kidney.

Pure aldosterone was isolated from beef adrenals in 1953 by collaborating groups in England and Switzerland; by 1956 its structure was established and it was synthesized from other steroids. There are several preparative procedures, but the high cost of the hormone and the availability of other mineralocorticoids greatly restrict its use in therapy.