This is an exploratory study to evaluate if SYN115 has an effect on Parkinson's disease as measured by clinical symptoms and brain images using magnetic resonance imaging (MRI) when a function test is administered.

This is a randomized, double-blind, placebo-controlled, two-way crossover study in which each patient will act as their own control. Each patient enrolled will receive both SYN115 (20 mg or 60 mg) and placebo separated by a minimum of one week washout between periods. An adaptive design will be used to determine if SYN115 elicits effects relevant to PD in the fewest number of patients by performing interim analyses in successive cohorts of patients receiving 60 or 20 mg.

Inclusion Criteria:

• Diagnosis of Parkinson's disease
• Hoen and Yahr stage 1-3
• On stable dose of anti-parkinsons treatment for 30 days prior to screening
• Age 40 to 75 years
• Sign an IRB approved informed consent
• Men and women agree to use adequate birth control
• ECG measurements are within normal limits
• Able to understand study requirements

Exclusion Criteria:

• Secondary Parkinson's (drug induced or post stroke)
• Received treatment with other investigational drug 30 days prior to study entry
• Using disallowed medications
• Significant neurological illness other than Parkinson's
• IQ less than 70 on IQ test
• MMSE score < or = 23
• History of psychosis or on anti-psychotic medication
• Current serious medical illness
• History of substance abuse
• History of head injury with loss of consciousness
• History of brain surgery
• Contraindications to MRI like claustrophobia, metal implants or other implantable devices
• Abnormal liver function tests and/or hepatitis or cholangitis
• Gilberts disease
• Pregnant or nursing
• Known hypersensitivity to SYN115