Patients will begin the treatment phase within 3 months of the dose-finding phase. After a brief physical examination, routine blood tests, and evaluation of parkinsonism symptoms, patients will begin taking either EMD 128130 tablets or capsules or a placebo (a look-alike pill with no active ingredient) twice a day, along with Sinemet, for 3 weeks. All participants will receive placebo at least 1 week during the study, and about four patients, selected at random, will receive only placebo the entire 3 weeks. Levodopa and apomorphine infusions will be repeated at the end of weeks 1, 2 and 3 of Phase 3. The procedure for the infusions will be the same as in the dose-finding phase.