TAS-4 is a potent and selective mGluR4 positive allosteric modulator with significant anti-Parkinson's disease activity. TAS-4 is able to show efficacy when used alone or in combination with l-DOPA. TAS-4 is able to reverse haloperidol-induced spasticity when administered alone. TAS-4 enhances the contralateral rotation behavior induced by l-DOPA in a dose-dependent manner. TAS-4 combined with low-dose l-DOPA shows anti-Parkinson's effects similar to full-dose l-DOPA without exacerbating abnormal motor side effects.