Some aspects of adrenocortical function were investigated in young male guinea pigs fed an ascorbic acid (AsA)-deficient diet for 7 days, followed by 0.1 mg AsA/100 g body weight/day for 4 days; pair-fed guinea pigs served as controls. Ninety minutes prior to killine, all guinea pigs received either an adrenocorticotropic hormone (ACTH) or saline injection, and 30 minutes prior to killing, all were injected with 20 muCi 45Ca/100 g body weight intraperitoneally. AsA restriction alone caused an 89% reduction in adrenal AsA concentration, but growth rate, adrenal weight and plasma ACTH were not different from those of pair-fed controls. Adrenal radiocalcium uptake, adrenal calcium content and plasma corticosteroids were similar in saline-treated guinea pigs restricted in AsA and the ACTH-treated controls, all of which were significantly higher than the values observed in saline-injected controls. Similar responses of the ACTH-treated controls and the saline-treated mildly deficient guinea pigs indicated that, at the adrenal AsA levels achieved (4.45 to 7.02 mg/100 g tissue), adrenal calcium and plasma corticosteroids increased significantly without the mediation of ACTH.