PCOS will be defined using criteria developed at the 1990 NICHD conference on PCOS3 - i.e., all women will have oligomenorrhea (eight or fewer menstrual periods annually) and hyperandrogenemia (elevated serum total or free testosterone concentration), and secondary causes of hyperandrogenism or ovulatory dysfunction will be excluded (see below: Entrance Criteria). All women will undergo a standard oral glucose tolerance test (OGTT) to screen for diabetes mellitus,16 but impaired glucose tolerance (IGT) will not be an exclusion criteria because of the high prevalence of IGT in this population.8,17-19 We intentionally will not screen the women for the presence of insulin resistance. Women with PCOS who have disorders associated with insulin resistance - such as hypertension21-23 or dyslipidemia21-23 - will not be excluded as long as they have been on a stable dose of medication for 6 months.