A Double-blind, Double-dummy, Placebo-controlled, Randomized, Three Parallel Groups Study Comparing the Efficacy, Safety and Tolerability of Pramipexole ER Versus Placebo and Versus Pramipexole IR Administered Orally Over a 26-week Maintenance Phase in Patients With Early Parkinsons Disease (PD).

The objectives of this trial conducted in early Parkinson's Disease (PD) patients are to determine the efficacy (as measured by the change from baseline to the end of the maintenance phase in the total score for the Unified Parkinson's Disease Rating Scale (UPDRS) Parts II and III combined), safety, and tolerability of Pramipexole Extended Release (ER) (in daily doses from 0.375mg to 4.5mg q.d.) in comparison to placebo, and to test for non-inferiority between the two formulations (ER and IR) of pramipexole. In addition, the efficacy of Pramipexole Immediate Release (IR) will be compared to placebo, for assay sensitivity