Placebo-Controlled Double-Blind Crossover Comparative Study of KW-6500

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