The follicular fluid (FF) in 91 follicles from 17 women treated with leuprolide acetate (LA) before stimulation with gonadotropins for in vitro fertilization were analyzed for estradiol (E2), progesterone (P), androstenedione, prolactin, and human chorionic gonadotropin (hCG) and compared with the concentrations in 128 follicles from 31 women treated with gonadotropins alone. The FF E2 concentration in LA-treated patients was significantly lower than in non-LA patients for all oocyte maturational stages. Follicles containing metaphase II oocytes had significantly lower concentrations of P and hCG in LA-treated patients. These differences persisted when analysis was limited to follicles whose oocytes fertilized normally. These data indicate that in the presence of LA, normal oocyte maturation can occur despite lower intrafollicular concentrations of E2 and P.