We report EEG findings in 15 presenile Alzheimer patients (probable Alzheimer's disease according to NINCDS-ADRDA criteria) and 15 age-matched controls. The quantitative EEG was analysed with respect to absolute power for each frequency band at each location accounting for EOG and EMG artifacts respectively. Compared to controls patients showed an increase of power in the slow frequency bands delta and theta which occurred quite uniformly over the different brain regions. In contrast, the decrease of the power of the fast frequency bands alpha 2, beta 1 and beta 2 was accentuated over temporo-parietal regions. In the fast bands patients had a rather flat topographic power profile. The alpha activity was on the average still of a rhythmic nature but the peak frequency was slowed. Differences in slow and fast frequency bands were more pronounced on the left hemisphere.