The secretion rate and plasma concentration of the adrenocortical steroid cortisol is modified in subjects treated with estrogenic and/or progestational steroids. The effects of contraceptive steroids on the secretion of ACTH are poorly documented, however, In the current investigation, we found that concentrations of ACTH and cortisol in plasma obtained at 0800--0900 h from a group of women with normal cyclic menses (n = 4) ranged from 78--120 pg/ml and 77--137 ng/ml, respectively. Although significant cyclic changes in the plasma levels of LH, FSH, 17 beta-estradiol, and progesterone occurred during the ovarian cycle, no obvious cyclic fluctuations in plasma levels of ACTH or cortisol were observed. In women treated with Norinyl 1 + 80 (1.0 mg norethindrone plus 0.08 mg mestranol), plasma concentrations of LH, FSH, 17 beta-estradiol, and progesterone were significantly lower (P less than 0.001) than plasma levels of these hormones in normal women during the ovarian cycle. The mean daily plasma concentrations of ACTH were significantly lower (P less than 0.001), whereas plasma cortisol levels were significantly higher (P less than 0.001) in women treated with oral contraceptive steroids compared to the levels of these hormones in the untreated ovulatory women.