Plasma progesterone, estrone, and estradiol concentrations were determined in peripheral and ovarian vein samples in 9 women 20 to 30 minutes after delivery of the placenta during cesarean section. Progesterone concentrations in the ovarian vein draining the corpus luteum were significantly higher than the contralateral side or the peripheral concentration, confirming the activity of the puerperal corpus luteum. Estrone concentrations showed no significant difference between peripheral and ovarian vein samples, indicating little or no ovarian estrone secretion. The estradiol concentrations of the ovarian vein samples were significantly higher than peripheral levels. This indicates ovarian secretion of estradiol in the puerperium by areas other than the corpus luteum.