Corticotropin-releasing hormone (CRH) is synthesized in most female reproductive tissues such as the ovaries and the uterus. In the non-pregnant uterus, it is mainly produced by epithelial cells of the endometrium. Recent in vitro experimental findings show that endometrial CRH is under the positive control of progesterone, participating in the decidualization process of endometrial stroma and the progression of blastocyst implantation. CRH is also produced in the thecal compartment of the human ovary, controlling ovarian steroid hormone biosynthesis. In the present study we compared the concentration of immunoreactive CRH (ir-CRH) in biopsies from proliferative and secretory human endometria, and from pre- and postmenopausal human ovaries. We found that the concentration of ir-CRH was significantly higher in the secretory (92 +/- 8 pg/mg protein; n = 10) than the proliferative (75 +/- 9 pg/mg protein; n = 12; p < 0.05) endometria. This observation supports the experimental in vitro findings associating endometrial CRH in intrauterine phenomena of the secretory phase of the menstrual cycle (decidualization and implantation). Additionally, we have shown that the concentration of ir-CRH was significantly higher in the premenopausal (125 +/- 12 pg/mg protein; n = 14) than the postmenopausal (100 +/- 12 pg/mg protein; n = 12; p < 0.05) ovaries, suggesting that ovarian CRH is related to normal ovarian function during the reproductive lifespan.