A study of event-related brain potentials (ERPs) in Alzheimer type dementia has been performed on 6 elderly subjects (mean age: 67.5). Patients were included if they met DSM-III criteria for primary degenerative dementia. They presented important loss of memory function (in short-term memory-STM and long-term memory-LTM) and impairment of attention. They were compared to two groups: normal elderly subjects with no memory trouble and no attention dysfunction (12 subjects, mean age: 66) and elderly subjects with minor trouble in STM and little attention disturbance (6 subjects, mean age: 68.5). The chosen procedure is a dichotic listening and selective attention paradigm. Three series of tone bursts occurred in counterbalanced order (frequent tones: 1,000 Hz, 2,000 Hz; rare tones: 1,450 Hz). Rare/frequent ratio was 10/90. Subjects were asked to press a key to the rare tones. During the task, ERPs are recorded with 16 electrodes (cross montage), using 2 different reference electrodes sites: nasion and 7th vertebra. Results are displayed with the use of chronograms, spatio-temporal maps, reaction time histograms. In Alzheimer's group compared to the 2 others: N100, N200, P300 are significantly delayed in latency. P300 has a smaller amplitude. In Alzheimer's, P300 distribution on the scalp is more frequently founded of greater amplitude on the frontal region than on the centro-parietal region while the opposite is found in normal subjects. These results suggest that memory trouble or attention dysfunction are well correlated with the abnormalities of the ERPs.