Patients with Parkinson's disease are missing the chemical neurotransmitter dopamine. This occurs as a result of destructive changes in an area of the brain responsible for making dopamine, the basal ganglia. Patients with the disease experience, rigid muscles, stooped posture, and a shuffling-type walk (gait).

In this study researchers plan to evaluate the effectiveness of the drug eliprodil for the treatment of Parkinson's Disease. Eliprodil works by blocking special receptors (NMDA) that are associated with the symptoms of Parkinson's Disease.

The objectives of this study are to evaluate the acute effects of the NR2B subtype-selective NMDA antagonist eliprodil on levodopa-associated motor response complications in patients with advanced Parkinson's Disease (PD).

All patients will carry a diagnosis of idiopathic Parkinson's Disease based on the presence of a characteristic clinical history and neurologic findings. Most will have relatively advanced disease with associated motor response complications.

Males and females between the ages of 18-75.

No presence or history of any medical condition that can reasonably be expected to subject the patient to unwarranted risk.

No patients with baseline QTc prolongation (greater than 440 msec).

No pregnant women nor those not practicing effective means of birth control.