This study involves study participants who have been clinically diagnosed with parkinsonian syndrome or who are at-risk for parkinsonian syndrome, have a family history of parkinsonian syndrome or exposure to environmental toxins potentially associated with parkinsonian syndrome. Participants will have brain imaging to assess dopamine transporter density. The imaging data coupled with family history and environmental exposure data may provide important information about potential risk factors for parkinsonian syndrome.

The brain imaging is conducted at the Institute for Neurodegenerative Disorders in New Haven, Connecticut. The imaging procedure occurs over a two day period.

On the first day participants are injected with [123I]ß CIT, an investigational radioactive material that localizes in the brain. Study participants will also have a thorough neurologic examination and standard neuropsychological testing, including testing of memory, concentration, abstraction and visual spatial functions.

Twenty-four hours later study participants return to the Institute for Neurodegenerative Disorders where an investigational scanning procedure will be used to obtain SPECT (single photon emission computed tomography) images of the brain.

Participants may be contacted to repeat these procedures every 12 to 18 months.

Inclusion Criteria:

• 22 years or older
• A clinical diagnosis of Parkinson's disease (PD), positive family history of PD and/or potential exposure to environmental toxins
• Normal screening laboratory studies

Exclusion Criteria:

• Pregnancy
• Psychiatric disease other than history of depression
• Significant medical disease including abnormalities on screening