Inclusion Criteria:

1. Subjects who meet DSM-IV criteria for panic disorder, with or without agoraphobia.
2. Subjects who have had at least one panic attack per week in each of the four weeks prior to the start of treatment and/or have a Mobility Inventory Score of 3.3 (alone) or 2.5 (accompanied).
3. Male or female subjects who are English-speaking between 18 and 55 years of age.
4. Female subjects who are not pregnant, or are surgically sterile or 2 years postmenopausal. If of childbearing potential, she must be using a medically-accepted method of birth control and agree to continue use of this method for at least 30 days after the study (i.e., barrier method with spermicide, steroidal contraceptive [oral, transdermal, and implanted, including Depo-Provera; contraceptives must be used in conjunction with a barrier method], or intrauterine device).
5. Subjects who are medically healthy (i.e. without a clinically significant unstable medical condition such as asthma, coronary artery disease, renal insufficiency, etc.)
6. Subjects who are able to give informed consent for participation.
7. Subjects who are able to be withdrawn from current panic disorder medication because it is ineffective.

Exclusion Criteria:

1. Subjects who have met DSM-IV criteria for substance abuse or dependence within six months of study entry must be excluded.
2. Subjects with a baseline Acute Panic Inventory (22 item test) score of 41 or higher on the test day must be excluded.
3. Subjects who are taking benzodiazepines, SSRIs, or medication that is effective for the prevention or treatment of the patient's panic disorder (i.e., no patient will be withdrawn for medication that is working for the purpose of entry into this study) must be excluded.
4. Subjects who are clinically depressed must be excluded.
5. Subjects who have received an investigational drug within 30 days (or within 5 half lives of the investigational drug) prior to test day must be excluded.
6. Subjects with epilepsy or other convulsive disorders must be excluded.
7. Subjects with a history of allergy or intolerance to benzodiazepines or related drugs (alprazolam, lorazepam, diazepam, etizolam, clonazepam, adinazolam) must be excluded.
8. Subjects who test positive for alcohol or have a positive urine drug screen for illicit or disallowed drugs must be excluded. Subjects should refrain from consuming alcohol for at least 48 hours prior to dosing.
9. Female subjects who are breastfeeding or have a positive pregnancy test must be excluded.
10. Subjects who have any other disease or condition, by history, physical examination, or laboratory abnormalities that in the investigator's opinion, would present undue risk to the subject, or may confound the interpretation of study results must be excluded.