In this study, the aim has been to characterize the profiles of progesterone, estradiol and follicular changes during postpartum period from parturition to first postpartum ovulation. Jugular venous blood was taken daily for progesterone and estradiol assay until first postpartum ovulation. The diameters of the follicles of the ovaries were recorded. The mean progesterone and estrogen concentrations markedly decreased (p < 0.05) during the 48 h after parturition. No correlation was observed between estradiol concentrations and the diameter of the largest follicle whereas a negative correlation was present between the number of follicles smaller than 20 mm and the number of follicles larger than 20 mm on the third and fourth days after postpartum. (C) 2007 Elsevier B.V. All rights reserved.