INCLUSION CRITERIA:

1. The study sample will consist of:

   Patients with a primary diagnosis of PTSD due to non-combat or combat related trauma according to DSM-IV.

   Subjects with non-combat related traumatic experiences without current PTSD and

   Healthy subjects without current or past history of psychiatric or major medical illness.

2. All subjects will be between 18 and 60 years old.
3. Male and female subjects will be included.
4. All subjects must be able to give written informed consent prior to participation in this study.
5. Patients with PTSD must score greater than or equal to 50 on Clinician-Administered PTSD Scale as a measure of PTSD symptom severity to be included in the study.
6. Patients who are not currently on medications for PTSD. (Patients will not be discontinued from effective medication for purposes of the study).
7. Patients who are nonresponders to other psychotropic drugs must have discontinued them for at least 2 weeks prior to the first PET scan. Medications will be discontinued under the supervision of the treating physician or a research psychiatrist listed in the protocol. (Nonresponders will be defined as subjects who continue to meet criteria for PTSD despite treatment with 30 mg equivalent of paroxetine for a minimum duration of six weeks).

7. All eligible subjects must be in good physical health as confirmed by a complete physical exam (including normal vital signs), electrocardiogram, neurological exam, and routine laboratory tests of blood and urine. [However, if patients have participated in other research studies or have had blood work through their primary MD within the last 6 months, these results will be used instead of repeating blood draws for inclusion into the study.]

EXCLUSION CRITERIA

1. Subjects with a clinically significant cardiovascular, pulmonary, endocrine, neurological, gastrointestinal illness or unstable medical disorder.
2. Patients who would be unable to comply with study procedures or assessments.
3. Subjects with primary trauma related to motor vehicle accidents.
4. Patients who meet DSM-IV criteria for alcohol and/or substance abuse or substance dependence within 6 months prior to screening.
5. Patients who are currently on fluoxetine (Justification: Washout from fluoxetine could take up to six weeks).
6. Patients who are currently at high risk for homicide or suicide.
7. Subjects with a current or past history of other axis I disorders like schizophrenia, schizoaffective disorder, bipolar disorder or dementia will be excluded from the study. However, those with a comorbid history of other Axis 1 disorder like major depression, dysthymia or panic disorder will be included in the study. Justification: Approximately 70% of subjects with PTSD have comorbid depression and or alcohol abuse; reviewed in 134. Restricting the sample to PTSD patients without depression will not accurately reflect the biology of this disorder].
8. Subjects with a history of peptic ulcer disease will be excluded. (Justification: Those with a history of acid peptic disease requiring antacids in the past will be excluded, although it is unlikely that a single dose of intravenous hydrocortisone could precipitate bleeding due to gastritis or peptic ulcer disease).
9. Women of childbearing potential who are not practicing a clinically accepted method of contraception or who have a positive pregnancy test or who are lactating.
10. Subjects who donated a Red Cross unit of blood within 60 days prior to participation in the study.