Patients with Parkinson's disease have low levels of the neurotransmitter dopamine. Dopamine is responsible for motor function and normal physical activity. Patients with Parkinson's disease typically suffer from tremors, rigid muscles, stooped postures, and walk with a shuffle. The drug levodopa acts as a replacement for dopamine and has been has been used effectively for over 30 years as treatment for Parkinsons disease. Because of its effectiveness, levodopa has been used to distinguish Parkinson's disease from other conditions that may resemble Parkinson's disease.

Traditionally, levodopa has been given as a pill. In this study, researchers would like to inject levodopa directly into a vein (intravenous) in order to diagnose cases of Parkinson's disease. This method provides immediate results and allows doctors to adjust the dose of levodopa very carefully. Because the intravenous method of giving levodopa is less practical than oral medication, it is not an available alternative for the routine treatment of Parkinson's disease. However, it may be useful for faster diagnosis of the disease and for determining effective doses of oral medication.