SUMMARY: Adrenalectomy caused a decrease in the rate of sebum secretion of male rats. On the other hand treatment with adrenocorticotrophic hormone (ACTH) produced a large increase in the rate of sebum secretion in hypophysectomized—castrated rats and restored it to the level in castrated rats. ACTH also stimulated sebum secretion in castrated rats after removal of the adrenals, although this increase was not significant. These findings suggest that a pituitary—adrenal—sebaceous gland system may exist. Adrenal androgens may play a significant part in this relationship. Although ACTH probably stimulates sebum secretion through its action on the adrenals it is possible that this pituitary hormone may have some direct effect on sebaceous gland activity.