Pupillary response test using dilute phenylephrine, a sympathetic agonist, and dilute pilocarpine, a cholinergic agonist, were performed in 24 patients with dementia with Lewy bodies (DLB), 40 patients with Alzheimer's disease (AD), and 23 normal elderly subjects. The mydriatic response to 0.5% phenylephrine was significantly greater in the DLB group than in the AD and control groups. The mydriatic change correlated inversely with the reduction in cardiac 123I-metaiodobenzylguanidine uptake. In contrast, miotic response to 0.0625% pilocarpine was significantly greater in the DLB and AD groups than in the control group. The pupil assay using combined phenylephrine and pilocarpine eye drop test may be useful in the detection of patients with DLB and AD and in distinguishing between them.