A single intravenous injection of 5 mg of hexadimethrine bromide to rats causes a significant decrease in the synthesis of aldosterone from 4- 14C-progesterone. The corticosterone production is reduced only in those adrenals with extensive necrosis by macroscopic examination. One mg of hexadimethrine bromide does not result in any marked change in the synthesis of aldosterone and corticosterone. In vitro added hexadimethrine bromide does not influence corticoid production except when very high doses are applied.