The effect of small bilateral hypothalamic lesions on the rate of aldosterone production by adrenal glands from sodium-deficient rats was studied in vitro. Lesions located in the median eminence (ME) or in the ventromedial nucleus (NVM) reduced both aldosterone and total corticosteroid production (in vitro). Lesions in the nucleus paraventricularis (NPV), the nucleus supraopticus (NSO) or the supraopticoneurohypophysial tract (Tr.S.) caused a substantial decrease in the rate of aldosterone production. Treatment with growth hormone (GH) restored aldosterone production by the adrenals of rats with NPV-lesions but had no effect in rats with lesions of the Tr.S. In contrast, treatment with vasopressin failed to affect aldosterone production of rats with NPV-lesions but restored the rate of aldosterone production of rats with lesions of the Tr.S. The increased water intake which resulted from lesions of the Tr.S. was normalized by the administration of vasopressin in doses which also restored aldosterone production in these animals. It is concluded that the hypothalamus controls aldosterone production in the sodium-deficient rat through various pituitary hormones.