The purpose of this study is to determine if Leukine (sargramostim) can be safely administered to Parkinson's disease patients for an extended period of time (56 days) and restore immune deficits seen in Parkinson's patients compared to controls. The development of magnetoencephalography (MEG) as a monitoring tool for PD will also be explored. At enrollment and repeating again at two 4-week intervals, whole blood from PD patients and controls will be obtained for analyses and the results will be used to calculate immune response profiles as a baseline for comparison after drug treatment. Physical examinations and motor assessments will also be performed on PD patients. After the 8-week baseline data collection, control participation will end and drug treatment of PD patients will begin. PD patients will be randomized, and half will receive drug and half will receive placebo. Leukine at a dosage of 6 µg/kg or saline as placebo will be administered by subcutaneous injection daily for 56 days (8 weeks). During drug treatment, PD patients will be monitored every two weeks by physical examinations, motor assessments, and blood analyses. As follow-up, four weeks after drug administration has stopped, subjects will again have physical examinations, motor assessments, and blood analyses. MEG will be performed on PD patients and controls at the start of drug treatment, and on PD patients at the end of the drug treatment period and 4 weeks after drug is stopped. In addtion, at the second cohort of 8 PD subjects, we will evaluate the potential Leukine-induced motor control and mobility improvements. Also, levels of the neurotransmitters glutamate, glutamine, serotonin, acetylcholine, GABA, norepinephrine and epinephrine in serum/plasma will be analyzed to correlate with changes in motor function and drug treatment.