Local variations in the ovarian renin-angiotensin system were investigated in peritoneal fluid (PF) during normal menstrual cycles and after ovarian stimulation with gonadotropins. PF was collected either during laparoscopy or by transvaginal aspiration before ovocyte retrieval for in vitro fertilization. Renin activity (RA) and angiotensin II immunoreactivity (Ang II-ir) were assayed in PF and simultaneously collected blood. The level of Ang II-ir was higher in PF than in plasma throughout the cycle, where as RA was in the same range of magnitude in the two compartments. In PF, Ang II-ir reached levels 2-5 times higher in the periovulatory period (days 12-14 and 15-17 of the cycle) than those found during the other stages of the cycle, whereas plasmatic Ang II-ir remained stable. No significant change could be demonstrated in RA throughout the cycle in either PF or plasma. Ovarian stimulation induced a strong elevation of Ang II-ir in PF, but not in plasma. High performance liquid chromatography revealed that the majority of Ang II-ir in PF was true Ang II. In conclusion, these results show a periovulatory elevation of Ang II in PF during the cycle and a more pronounced rise after treatment with gonadotropins. These observations support the involvement of Ang II in the process of ovulation or fecundation.