The purpose of this double-blind, placebo controlled study is to evaluate the safety and effectiveness of an investigational Parkinson's disease drug in patients with advanced disease who are not well-controlled on their L-dopa medication.

Inclusion Criteria:

• Idiopathic Parkinson's disease
• Modified Hoehn and Yahr Scale Stages II - IV
• Stable dose of L-dopa for at least 4 weeks prior to screening.
• Lack of control with L-dopa therapy.
• Women of child-bearing potential must use a clinically accepted form of birth control.

Exclusion Criteria:

• Significant and/or uncontrolled medical conditions (excluding Parkinson's disease) within 3 months of screening.
• Any abnormality, at screening, that is considered clinically relevant by the Investigator.
• Dementia
• Use of dopamine agonists within 4 weeks of screening visit.
• Participation in other investigational drug studies.

Patient-level data for this study will be made available through www.clinicalstudydatarequest.com following the timelines and process described on this site.