This is a pilot project to test the feasibility of developing an FSH stimulation test. There is a need for a sensitive and specific marker to detect ovarian insufficiency early in its course. FSH stimulates inhibin B production by the granulosa cells of the cohort of ovarian follicles; serum inhibin B in turn participates in the negative feedback loop regulating FSH secretion. This protocol is characterizing the normal FSH-stimulated serum inhibin B response to a single subcutaneous injection of 300 IU human recombinant FSH given on day 2 to 4 of the menstrual cycle. In preliminary analysis under this protocol we have demonstrated that FSH-stimulated serum inhibin B levels measured at 24 hours after injection is a more robust marker of functional ovarian age than ovarian follicle count by transvaginal ultrasound, basal serum Mullerian Inhibiting Substance (MIS) levels, or basal serum FSH levels. Multiple regression analysis has revealed that FSH-stimulated inhibin B, FSH-stimulated estradiol, and basal FSH contribute significantly to an ability to predict functional ovarian age (as approximated by chronological age). The resulting regression equation relating these three parameters with age has a correlation coefficient of 0.742 and a coefficient of determination of 0.551. The protocol is now evaluating the reproducibility of this test and the feasibility of generating normative data in young women between the ages of 18 and 25. The results of this study may define parameters that could lead to earlier diagnosis and treatment of premature ovarian insufficiency.