The experiments on adult (4-6 months) and old (28-30 months) rats revealed changes that develop in old age in various links of the regulatory system of aldosterone secretion: the hypothalamic-hypophyseal control of mineralocorticoid secretion decreased, and the sensitivity of the glomerular zone to ACTH, vasopressin, and K+, as well as that of the myocardium, skeletal muscle and kidney to aldosterone increased. Changes in tissue sensitivity to aldosterone may be due to the increased affinity of mineralocorticoid receptors to aldosterone in old age.