The concentrations of unconjugated estrone (E1), estradiol (E2), testosterone (T), androstenedione (A) and progesterone (P) were measured in peripheral and ovarian venous plasma collected from 18 healthy women on days 7–30 of the menstrual cycle at the time of elective tubal ligation. An additional 4 steroids, pregnenolone, 17α-hydroxyprogesterone (17-OHP), 20α-dihydroxyprogesterone (20-OHP) and dehydroepiandrosterone (DHEA), were measured in ovarian venous plasma. In 2 subjects, one in the follicular phase and one in the luteal phase, blood was obtained from both ovaries. There was evidence of secretion by the ovary of all the steroids measured. Of the C18 and C19 steroids, E2 and A, respectively, were secreted by the ovary in largest amounts. There was a wide range of concentration of each steroid in ovarian venous plasma collected at the same time of the cycle from different subjects. High concentrations of E2 were associated with high levels of E1, T and A. DHEA appeared to be higher in plasma from the less actively secreting ovary. Equally high values of all these steroids were found in specimens from both phases of the cycle. There clearly was secretion of progesterone in the luteal phase from the ovary containing the corpus luteum. In the subject where bilateral sampling was performed, the ovary that did not contain the corpus luteum secreted lesser, though still significant, amounts of P than the one containing the corpus luteum. In the follicular phase, there was a suggestion of secretion of P in 2 cases. In 3 of 4 subjects in the follicular phase in which 17-OHP was measured, it was increased; in one of these, 17-OHP was higher in blood from the ovary secreting the smaller amount of estrogen. In the luteal phase, high levels of 17-OHP were found in some subjects. The relationship between 17-OHP and P or E2 was not consistent. The range of concentrations of all the steroids in the peripheral plasma was much less than in the ovarian plasma. The ratios of A/T and E2/E1 in ovarian vein plasma were 4–6 times higher than in peripheral vein plasma.