Distributions of the amplitudes and the latencies of N100, P200, N200, P300 and mismatch negativity (MMN) were studied. The P300 latency was delayed in patients with dementia of the Alzheimer type (DAT) and patients with vascular dementia (VD). The N200 latency was delayed on Pz in DAT patients, and on Fz in VD patients. MMN latency was delayed on Pz in DAT patients. The P300 amplitude was low on Pz in DAT patients. The N100 amplitude was low in VD patients on Pz. These findings show the difference in cerebral lesions between DAT and VD. We suggest that studies of P300 amplitude, N200 latency, MMN latency and N100 amplitude distribution would be useful in differential diagnosis in patients with dementia.