OBJECTIVE: Bile acids are the end products of cholesterol degradation. They serve important roles in cholesterol trafficking in the gastrointestinal and hepatobiliary systems and their synthesis is tightly regulated. Previously, we demonstrated for the first time the presence of bile acids in human ovarian follicular fluid (FF) from 43 patients undergoing in vitro fertilization (IVF). The aim of this study was to determine if nuclear receptors that are known to regulate bile acids synthesis are present in mature human ovarian follicles, oocytes, and granulosa cells (GC). DESIGN: Observational cohort study. MATERIALS AND METHODS: FF and GC from large follicles (>16mm) from young (<35 years) and older (≥40 years) IVF patients were obtained at the time of vaginal oocyte retrieval. FF very low density lipoprotein, low density lipoprotein, high density lipoprotein, and cholesterol microparticles were isolated by isopicnic ultracentrifugation. Discarded, nonfertilized human oocytes were obtained separately. FF and cholesterol fractions were analyzed by western blot for the bile acid receptor Farnesoid X Receptor (FXR) and other receptors known to regulate the bile acid synthesis pathway including 9-cis Retinoic X Receptor (RXR), Liver X Receptor α (LXRα), Liver Receptor Homolog 1 (LRH-1), and Nuclear Receptor Short Heterodimer Partner (SHP). GC were analyzed by immunofluorescence (IF) for FXR, RXR and SHP. Oocytes were analyzed by IF for FXR, RXR, and SHP. RESULTS: The bile acid receptors RXR, LXRα, and LRH-1 are present in FF from old and young patients as demonstrated by western blot. There appears to be more RXR and LRH-1 in the FF of young patients and more LXRα in FF from old patients. FXR and RXR are present in the nuclei of human granulosa cells by IF analysis. FXR, RXR, and SHP are present in the cytoplasm of nonfertilized human oocytes as demonstrated by IF. CONCLUSIONS: This is the first demonstration that the bile acid receptor FXR and the nuclear receptors LXRα, LRH-1, and SHP are components of human ovarian follicles. The presence of both bile acids and nuclear receptors known to regulate bile acid synthesis and transport in ovarian follicles suggests that the presence of bile acids in follicular fluid is not incidental. Bile acids may serve an important role in the regulation of intrafollicular steroid production. The function of bile acids and these nuclear receptors in human ovarian follicles remains under investigation.