Ovarian secretion of hormones was determined at hourly intervals for a period of 9 h following the administration of human chorionic gonadotropin (hCG) to estrous rabbits. Blood flow to the ovary was measured with radio-labeled microspheres immediately before peripheral and ovarian vein blood samples were obtained. The ovarian vein plasma concentration and secretion rates of estradiol-17β (E2) and testosterone (T) rose sharply at the 2 h period. By 4 h, when ovarian blood flow reached its maximum, the secretion rate of E2 and T reached a second peak. Secretion rates of estrone (E1), androstenedione (A), progesterone (P) and 20α-dihydroprogesterone (20α-OH-P) showed only a single peak at the 4 h period. There was no significant change in the peripheral blood levels of E1, E2 and A and there was a small rise in T between the second and fourth hours; in contrast, an increase in P noted in the first hour was sustained up to the eighth hour, while 20α-OH-P was elevated throughout with peaks at 2, 5 and 9 h.