A systematic autonomic dysfunction observed among patients with dementia with Lewy bodies (DLB) has recently attracted close attention. Here, we compare cardiovascular and pulmonary autonomic functions among patients with DLB, patients with Alzheimer's disease, and healthy control subjects. All 15 DLB patients demonstrated severely low ventilatory response to hypercapnia, whereas none of the other subjects demonstrated abnormal results. The majority of the DLB patients showed impaired heart rate variability, low uptake on (123)I-metaiodobenzylguanidine myocardial scintigraphy, and orthostatic hypotension. Ventilatory response to hypercapnia as a marker of respiratory autonomic function is a promising diagnostic tool for DLB.