Inclusion Criteria:

1. Subjects must provide written informed consent prior to the initiation of any study related procedures;
2. Age 40 to 80 years;
3. Subjects must have had upper extremity tremor for < 3 years duration.

Exclusion Criteria:

1. Any clinically significant acute or unstable physical or psychological illness based on medical history or physical examination at Visit 1, as determined by the PI;
2. Any unexpected clinically significant abnormal laboratory or electrocardiogram (ECG) results obtained at Visit 1 and as determined by the PI;
3. Any history or drug, narcotic, or alcohol abuse within 2 years before the date of informed consent, as defined by the Diagnostic and Statistical Manual of the American Psychiatric Association, Fourth Edition, revised DSM-IVR, American Psychiatric Association, 1994;
4. Positive drug screen for opiates, cocaine or amphetamines at Visit 1;
5. Positive pregnancy test at Visit 1 and/or Visit 3;
6. Participation in an investigational drug or device clinical trial within 30 days prior to the date of informed consent;
7. Previous participation in any 123I-ALTROPANE® trial;
8. Any exposure to radiopharmaceuticals within 30 days prior to the date of informed consent;
9. Breast-feeding;
10. Inability to lie supine for 1 hour;
11. Any thyroid disease other than treated hypothyroidism;
12. Known sensitivity or allergy to iodine or iodine containing products;
13. Treatment within the 4 weeks before the date of the informed consent with buproprion, methylphenidate or amphetamine;
14. Any treatment with anti-Parkinson's drugs within 4 weeks before the date of informed consent.

Subject eligibility based on exclusion criteria 1, 2, 3, 4, and 20 will be confirmed at Visit 3 prior to dosing.