OBJECTIVE:To evaluate the presence of CA-125 in follicular fluid (FF) and its possible correlation to FF estradiol (E2), progesterone (P) and testosterone (T) and in vitro fertilization and embryo transfer (IVF-ET) outcome. DESIGN:Twenty-eight patients undergoing IVF-ET were randomly chosen and 123 FF were sampled. SETTING:Clinical IVF-ET program and immunology laboratory for tumor diagnosis in a university tertiary care center. PATIENTS:Pure tubal factor patients treated by midluteal (long) gonadotropin-releasing hormone agonist protocol coupled with follicular phase human menopausal gonadotropin. INTERVENTIONS:Transvaginal follicular aspiration followed 48 hours later by ET. MAIN OUTCOME MEASURES:The 28 treatment cycles resulted in six gestations including five take-home infants. The mean levels (+/- SD) were 30.1 +/- 66.0 U/ML for CA-125, 28.5 +/- 58.1 ng/ML for E2, 2,360.5 +/- 2,846.3 ng/ML for P, and 7.22 +/- 7.08 ng/ML for T. The FF CA-125 levels were found to be widely divergent in different follicles of the same patient. There was no significant correlation between FF CA-125 and E2, P, T, oocyte fertilization, embryo quality, and pregnancy rates. CONCLUSIONS:CA-125 exists in significant amounts in FF of periovulatory follicles of IVF-ET patients. Intrafollicular CA-125 secretion is neither interrelated to follicular steroidogenesis nor is correlated to the outcome of IVF-ET.