INCLUSION CRITERIA:
Subjects may be included in the study only if they meet all of the following criteria:
1. Male or female subjects, 18 to 65 years.
2. Female subjects of childbearing potential must be using a medically accepted means of contraception.
3. Each subject must have a level of understanding sufficient to agree to all required tests and examinations and sign an informed consent document.
4. A negative urine toxicology.
5. Subjects must fulfill the criteria for PTSD as defined in DSM-IV (309.81), which should be the primary diagnosis. Diagnoses are based on clinical assessment and confirmed by structured diagnostic interview SCID-P.
6. Duration of illness of PTSD for at least 3 months.
7. Subjects must have an initial score at Visit 1 and Visit 2 of at least 50 on the CAPS for PTSD Studies.
8. Subjects must not have a decrease in the total score of CAPS of greater than 25% during washout (between Visits 1 and 2).
EXCLUSION CRITERIA:
Subjects will be excluded from the study for any of the following reasons:
1. Presence of psychotic features.
2. Participation in a clinical trial of another investigational drug within 1 month (30 days) prior to study entry (Visit 1).
3. Female subjects who are either pregnant or nursing.
4. Serious, unstable illnesses including hepatic, renal, gastroenterologic, respiratory, cardiovascular (including ischemic heart disease), endocrinologic, neurologic, immunologic, or hematologic disease.
5. Subjects with uncorrected hypothyroidism or hyperthyroidism.
6. Previous treatment with NK1 receptor antagonist.
7. DSM-IV substance abuse or dependence within the past 90 days.
8. Treatment with an injectable depot neuroleptic within less than one dosing interval between depot neuroleptic injections prior to Visit 2.
9. Treatment with a reversible MAOI, guanethidine, or guanadrel within 1 week or with fluoxetine within 6 weeks prior to Visit 2.
10. Treatment with any other concomitant medication with primarily CNS activity.
11. Treatment with clozapine or ECT within 12 weeks prior to Visit 2.
12. Current diagnosis of schizophrenia or other psychotic disorder, bipolar disorder, other Axis I disorder (except for major depressive disorder, dysthymia and other anxiety disorders that followed exposure to the trauma) as defined in the DSM-IV.
13. Patients who are currently at high risk for homicide or suicide, a score greater than 4 on item 10 of the MADRS.
14. Current or planned litigation regarding the traumatic event.
Patients will not be allowed to receive structured psychotherapy during the trial.