In order to assess the ovarian and adrenal contribution to peripheral levels of testosterone (T), 5α-dihydrotestosterone (DHT), androstenedione (A), dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S) in premenopausal women, six normally menstruating subjects were studied during two complete mentrual cycles. The first cycle served as control and dexamethasone was given during the second cycle. Plasma cortisol (F) was measured to assess the degree of adrenal suppression. Plasma progesterone (P), 17-hydroxyprogesterone (17-P) and estradiol-17β (E₂) served as indirect indices of ovulation. The estimation of plasma LH located the midcycle peak and the data for all steroids were evaluated in relation to the LH peak. All cycles studied were apparently ovulatory, as judged by the plasma levels of P, 17-P and E₂. Dexamethasone treatment had no detectable effect on the levels of these three steroids. Assuming that dexamethasone suppressed completely the adrenal cortex and had no detectable effect on ovarian steroidogenesis, the following conclusions were made: 1) the adrenal contribution to peripheral T, DHT, A, DHEA and DHEA-S is relatively constant within random fluctuations throughout the menstrual cycle; 2) the ovarian contribution of peripheral T, A and DHEA-S reaches maximum levels at midcycle, whereas ovarian contribution to peripheral DHT and DHEA does not seem to be influenced by the menstrual cycle; 3) the ovary and the adrenal cortex contribute equally to peripheral T, DHT and A, except for peripheral A at midcycle when the ovarian contribution is twice that of the adrenal; and 4) peripheral DHEA and DHEA-S originate predominantly from the adrenal cortex which contributes 80% of DHEA and greater than 90% of DHEA-S.