Somatosensory ERPs and short latency somatosensory evoked potentials (SSEPs) were studied in patients with dementia of the Alzheimer type (DAT), those with vascular dementia, demented and non-demented patients with Parkinson's disease, and healthy control subjects. In control subjects, latencies of N140, P200, N240 and P300 components increased with age at a rate of 0.2, 0.2, 0.6 and 1.5 msec/year, respectively. Patients with DAT and demented patients with Parkinson's disease had normal SSEPs as well as normal P100, and N140 latencies, but patients with vascular dementia showed prolonged N140 and P200 latencies in addition to a prolonged central conduction time (CCT). Analysis of N140 and P200 components of somatosensory ERPs may be important for evaluation of patients with vascular dementia. In patients with DAT, those with vascular dementia and demented patients with Parkinson's disease, the P300 latency was significantly prolonged compared with that in age-matched control subjects. However, the P300 latency did not show any significant differences among the groups of demented patients.