Inclusion Criteria:

- Between the ages of 25 and 45 and pre-menopausal;

- Non-lactating and not pregnant

- able to follow the schedule of procedures

- able to freely provide informed consent

- have clinically acceptable physical examination and safety laboratory studies

Exclusion Criteria:

- current use of any form of systemic contraceptive

- have self-reported irregular menstrual cycles

- intercurrent illness(es) detected on the screening physical

- unwilling or unable to use barrier methods of contraception

- have evidence of endometrial polyps or myomata on TVU/SIS that would interfere with
endometrial thickness measurement

- detection of ovarian cyst(s) during adnexal examination on screening TVU/SIS
measuring greater than 5 cm

- have history of, or current cancer, on any form exclusive of basal cell carcinoma

- BMI >= 35

- history of alcohol or drug abuse in the past 5 years

- unwilling or unable to undergo study procedures within the necessary time frames

- history or current liver abnormalities as defined by ALT or AST > 2X ULN

- treated or untreated diabetes defined as fasting blood sugar >= 126 mg/dL

- untreated hypertension

- impaired renal function by estimated creatinine clearance < 80mL/min

- have estradiol levels < 20 pg/ml and FSH levels > 40 mIU/mL or

- have a history of adverse reaction any aromatase inhibitor