The authors analyzed whether nondemented (PD) and demented Parkinson patients (PDD) and patients with dementia with Lewy bodies (DLB) respond similarly in the levodopa test (LDT). Percentage of motor improvement was similar in the three groups; the proportion of patients with 10% and more improvement was greater in PD than in PDD and DLB. Positive LDT was predictive for favorable response in chronic levodopa treatment, but also some nonresponsive demented patients profited from chronic levodopa therapy.