This is a placebo-controlled double-blind crossover comparative study of KW-6500 in Parkinson's disease patients with motor response complications on levodopa therapy. The efficacy of KW-6500 is evaluated using the change of UPDRS part III score at double blind period after 12 weeks subcutaneous self-injections.

Inclusion Criteria:

• Patients who have given written informed consent
• Patients who have Parkinson's disease
• Patients who have been on a stable regimen of levodopa plus at least one other antiparkinsonian agent and who have OFF state
• Patients who meet stage 4 or 5 while in the OFF state and stage 0 to 3 while in the ON state on the Modified Hoehn and Yahr Scale
• Patients who have experienced a 30% or more improvement in Unified Parkinson's Disease Rating Scale (UPDRS) partⅢ score when tested for responsiveness to levodopa during the baseline period
• Patients who have at least one OFF state per day
• Patients who can understand the expression of OFF state, ON state, and dyskinesia
• Patients or their families have a desire for self-injection of KW-6500

Exclusion Criteria:

• Patients with an illness of the cardiac, hematologic, hepatic, renal, pancreatic, metabolic, respiratory, gastrointestinal, endocrinologic, or neurologic system (excluding Parkinson's disease)
• Patients with orthostatic hypotension
• Patients with a history of intolerance to morphine or its derivatives, sulfur, sulfur-containing pharmaceutical products, or sulfite
• Patients with a history of malignant syndrome
• Patients with a diagnosis of cancer or evidence of continued disease
• Patients who do not test negative in the direct Coombs' test
• Pregnant or lactating women, women who are planning to have children, women who test positive in the pregnancy test, or women who cannot adhere to a reliable method of contraception
• Patients who have received MAO inhibitors except selegiline
• Patients with a history of mental disease (excluding psychiatric symptoms associated with Parkinson's disease)
• Patients with a Mini-Mental State Examination score of 23 or less
• Patients who are taking antipsychotics or central dopamine antagonists (excluding domperidone)
• Patients who are receiving methyldopa or 5-HT3 receptor antagonists
• Patients who are receiving reserpine or papaverine
• Patients who have had a neurosurgical operation for Parkinson's disease
• Patients who have had transcranial magnetic stimulation
• Patients with a history of drug or alcohol abuse or dependence