A cross-over study, where ND0611 or placebo will be tested on top of 3 different LD/CD dosage forms. Safety and tolerability, pharmacokinetic profile of levodopa and carbidopa and the potential clinical effect of ND0611 will be explored in subjects with PD and motor fluctuations.

Inclusion Criteria:

1. Men and women with idiopathic Parkinson's disease
2. Subjects must experience motor fluctuations associated with LD/CD dosing
3. Modified Hoehn and Yahr stage < 5
4. Subjects must be taking optimized and stable levodopa/dopa decarboxylase inhibitor therapy
5. Women must be postmenopausal, surgically sterilized, or using adequate birth control. Women of childbearing potential must have a negative pregnancy test (serum beta-HCG) at screening.
6. Subjects must be age 30 or older.
7. Subjects must be willing and able to give informed consent.

Exclusion Criteria:

1. Subjects with a clinically significant or unstable medical or surgical condition
2. Subjects with clinically significant psychiatric illness.
3. Pre-menopausal women, not using birth control method.
4. Subjects who have taken experimental medications within 60 days prior to baseline.
5. Subject who have undergone a neurosurgical intervention for Parkinson's disease (e.g., pallidotomy, thalamotomy, transplantation and deep brain stimulation).