Patients with Parkinson's disease (PD) by definition benefit from treatment with the dopamine precursor levodopa. However, after 5 years of therapy 50% of patients experience motor response complications (MRC's): the benefit from each dose becomes shorter (wearing-off fluctuations), more unpredictable (on-off fluctuations) and associated with involuntary movements (dyskinesias). In addition these patients suffer from fluctuations in motor function that are inherent to the disease itself. Recent findings have lead to the suggestion that hyperfunction of NMDA receptors on striatal efferent neurons, as a consequence of chronic non-physiologic dopaminergic stimulation, contributes to the pathogenesis of MRC's. In PD patients blockade of striatal glutamate receptors with several NMDA-antagonists improve MRC's. With progression of PD the severity and complexity of MRC's magnify, obfuscating their pattern and their relation to the medication cycle. Only through detailed history taking and patient education will the physician be able to clarify the situation and establish a rational, targeted approach to the treatment of patients with advanced PD complicated by motor fluctuations and dyskinesias.