The rapidity with which progesterone (P) suppresses daytime lutenizing hormone (LH) (and by inference gonadotropin releasing hormone (GnRH)) pulse frequency is unknown. We propose to assess this further using a randomized, cross-over, placebo-controlled study. Ovulatory women will begin E2 patches on day 4-8 of the cycle, while women with PCOS will begin E2 patches either on day 4-8 of the cycle or at least 8 weeks post-menses. After 3 d of E2 administration, women will undergo a 24-h sampling study in the GCRC. Beginning at 2000 h, blood for LH, FSH, E2, P, and T will be obtained over a 24-h period. After 10 h of sampling, either oral micronized P (100 mg p.o.) suspension or placebo suspension will be administered (according to randomization). At the completion of sampling, E2 patches will be discontinued. During a subsequent menstrual cycle (or after at least 3 weeks in oligomenorrheic PCOS), subjects will undergo another GCRC study identical to the first (including pretreatment with E2) except that oral P will be exchanged for placebo or vice versa in accordance with the crossover design. We will assess the acute effects of progesterone on LH frequency, with secondary endpoints being mean LH, LH pulse amplitude, and mean follicle-stimulating hormone (FSH). We propose two primary hypotheses: (1) administration of P (at 0600 h) to normally cycling adult women during the follicular phase will result in a demonstrable suppression of daytime LH (and by inference GnRH) pulse frequency within 12 hours; (2) administration of P (at 0600 h) to women with PCOS will result in less suppression of daytime LH pulse frequency than in ovulatory women without PCOS. A secondary hypothesis is that augmentation of LH amplitude after P administration will be less in PCOS compared to normal controls.