The purpose of this study is to determine why obese women have lower hormone levels and less fertility than women of normal body weight. The proposal will examine the reproductive system at the level of the brain and the ovary to define the changes that happen leading to lowered hormone production. Women will be studied throughout a menstrual cycle and given medications that will test how well their pituitary gland can make hormones that stimulate the ovary (luteinizing hormone (LH) and follicle stimulating hormone (FSH)). They will also be given a medication to abolish estrogen production in the body and their response to this medication will be assessed. Finally, the ovary's ability to produce progesterone after ovulation will be examined.