The primary objective is to assess the effect of SR57667B at the dose of 4 mg/d on the progression of Parkinson symptoms in patients with early PD. The primary outcome will be the time to progression of disability warranting initiation of L-dopa or a dopamine agonist. Secondary outcomes will comprise assessments of symptoms, activities of daily living and global clinical status.

Multinational, multicenter, randomized, parallel-group, double-blind, phase II study.

Inclusion Criteria:

• Male or female outpatients.
• Age >=35 years at screening.·
• Diagnosis of Parkinson's syndrome, on at least two of the three key Parkinson's symptoms, i.e. resting tremor, bradykinesia and rigidity.
• Duration of the disease of less than 3 years since diagnosis·
• Modified Hoehn and Yahr stage <= 2.5.
• Untreated patients.
• Generally healthy and ambulatory.
• Patient has given his informed written consent and is capable of following study procedures.

Exclusion Criteria:

• Any indication of forms of parkinsonism other than PD.
• Severe resting tremor.
• Presence of either dyskinesia, fluctuations, or loss of postural reflexes·
• Treatment with L-Dopa, dopamine agonist, amantadine, anticholinergics, catechol-o-methyltransferase (COMT ) inhibitors, selegiline, dopamine receptor antagonists, catecholamine depleters, indirect dopamine agonists or alphamethyldopa.
• Electroconvulsive therapy (ECT).
• Use of CYP3A4 strong, and moderate inducers or inhibitors.
• Participation in another clinical trial with an investigational drug within two months prior to randomization.
• Dementia, uncontrolled depression, psychotic disorder.
• History of substance-related disorders including alcohol or other substance use disorders.
• Females of child bearing potential.
• Evidence (detected by history, physical examination and/or laboratory/ECG tests) of any clinically significant or unstable medical disorder that could interfere with the patient's participation in the clinical trial; interfere with the absorption, metabolism or excretion of the study medication; or interfere with the evaluation of the study drug.
• Alterations of laboratory tests or ECG findings of potential clinical significance.