In order to assess the ovarian contribution to peripheral steroid levels during the menstrual cycle, the serum levels of various steroids were measured daily during a complete menstrual cycle in a bilaterally adrenalectomized woman. The following steroids were measured: progesterone (P), 17-hydroxyprogesterone (17-OHP), pregnenolone (5Δ-P), 17-hydroxypregnenolone (17-5Δ-P), dehydroepiandrosterone (DHEA), it's sulfate (DHEA-S), testosterone (T), 5α-dihydrotestosterone (DHT), androstenedione (A), estrone (E1), estradiol-17β (E2), and cortisol. Plasma cortisol and 17-5Δ-P were undetectable throughout most of the study period. However, the remaining steroids studied were measurable. The patterns and levels of the steroids observed in the adrenalectomized subject suggest the following when compared to patterns and levels of the same steroids during menstrual cycles of intact women. The progestins, P and 17-OHP, are secreted by the ovary not only during the luteal phase but also throughout the follicular phase. The steroid 17-5Δ-P originates in the adrenal cortex almost exclusively during the follicular phase and most of the luteal phase. In the subject studied, the ovary secreted 5Δ-P in a pulsating fashion with peaks occurring every 5 to 6 days. The ovary and adrenal cortex both contribute significantly to the peripheral levels of the androgens, T, DHT, A and DHEA. The adrenal cortex contributes more than 90% of the peripheral DHEA-S. Ovarian contribution to plasma DHEA-S, T, and A is maximal at midcycle. During the menstrual cycle, plasma E2 comes from the ovary almost exclusively. Both the ovary and the adrenal cortex seem to contribute to the peripheral levels of E1.