Women diagnosed with Bipolar Disorder, between 18-40 years of age, who are currently treated with a mood stabilizing agent for a period of at least 3 months and are not taking birth control pills currently. Participants must be willing to travel to Stanford University (near San Francisco, CA) at their own expense for study visits.

Inclusion Criteria for All Participants:

• Have been menstruating for at least 4 years prior to study entry
• Participants must be willing to travel to Stanford University at own expense for study visits

Inclusion Criteria for Bipolar Disorder Participants:

• Participants should have a diagnosis of Bipolar I, Bipolar II, or Bipolar not otherwise specified (NOS), and be under the treatment of a physician who can be contacted in case of an emergency
• Current treatment with any mood-stabilizing agent for a period of at least 3 months (e.g., divalproex sodium, lithium, other mood stabilizer, or atypical antipsychotic)

Inclusion Criteria for Healthy Controls:

• No past or present diagnosis of mental illness

Exclusion Criteria for All Participants:

• Current alcohol or substance abuse or dependence within 6 months prior to study entry
• Meets criteria for another DSM-IV Axis I disorder
• Contraceptive steroid use within 3 months prior to study entry
• Current use of medication that may affect steroid metabolism
• Menopausal
• Endocrine disease such as diabetes or hypothyroidism
• Uncontrolled medical illness
• History of long-term corticosteroid use
• Organic mood disorder
• Pregnancy or breastfeeding within 3 months prior to study entry