A novel approach is introduced to examine EEG coherence in different frequency bands of 17 locations from the 10-20 system. Fifty patients with clinically diagnosed Alzheimer's disease were compared with 42 age-approximated non-demented controls. We determined the average coherence between individual electrodes and all neighbouring electrodes. Coherence was decreased in the sample of demented patients and this effect was most pronounced in the frontal and central derivations of the theta, alpha and beta frequency bands. The results can be interpreted as the effects of neuronal loss and neocortical disconnection.