The purpose of the research is to study brain structure, function and chemistry of patients with bipolar disorder who are receiving lithium, an FDA-approved treatment for bipolar mania, in order to better understand who benefits from treatment and why they respond to medications. Studying this may help improve treatment and outcome in patients with bipolar disorder.

Inclusion Criteria- bipolar patients (Manic=, depressed=60; 30 patients/year):

1. The patient meets DSM-IV criteria for type I bipolar disorder, manic or mixed, or depressed.
2. The patient has an index Young Mania Rating Scale (YMRS)total score >15 or Montgomery Asberg Rating Scale (MADRS) total score >20.
3. The patient is between 15 and 55 years old.

Inclusion Criteria- Healthy subjects (N=40):

1. Healthy subjects will be between the ages of 15 and 55 years.
2. Healthy subjects will have no history of any Axis I psychiatric disorder.
3. Healthy subjects will have no first-degree relatives with affective or psychotic disorders.

Exclusion criteria: All subjects will be excluded from participation for the following reasons.

1. Any medical or neurological disorder that could influence fMRI and MRS results.
2. A history of mental retardation or an estimated IQ total score <85.
3. An MRI scan is contraindicated in the subject for any reason, including psychological impediments to being inside the MR scanner.
4. The patient cannot attend follow-up visits.