Investigational Parkinson's Disease In Patients Not Well Controlled On L-dopa

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.