Subjects will undergo another GCRC study identical to the first (including pretreatment with E2, outpatient blood draw 4-5 days before admission, etc.), except that oral P will be exchanged for placebo or vice versa in accordance with the crossover design. (Subjects will again begin E2 patches on the evening of cycle day 4-8 [controls or PCOS] or >= 8 weeks post-menses [PCOS only].) In this way, we will be able to standardize any change in GnRH pulse frequency after P administration to any change in GnRH pulse frequency after placebo administration.