Brains of normal controls and patients with primary degenerative dementia were investigated for choline acetyltransferase (ChAT) activity in the frontal, temporal and parietal cortex, hippocampus, amygdala and thalamus. A few patients with Alzheimer's disease were unusual as the cholinergic marker was unaffected, except in the amygdala. Other patients with dementia and undiagnosed neurodegenerative disorder had elevated cortical ChAT activity. The interpretations offered are: (a) the syndrome of dementia and Alzheimer pathologic change precedes significant loss of cortical cholinergic innervation; (b) denervation in dementia can occur early in olfactory areas, exemplified here by the amygdala; (c) dementia is associated with the loss of non-cholinergic structure. An indication of structures involved was given by loss of a marker of excitatory amino acid-releasing neurones.