Severe dementia is associated with frequent psychiatric and behavioural disturbances in addition to marked cognitive and functional deficits. Research to determine a neurochemical understanding of dementia over the last three decades has generated therapeutic strategies which improve patients' cognition and activities of daily living. Different key dementia syndromes have been shown to have distinct neurotransmitter biochemical patho-logy, with important implications for therapy. The current review focuses predominantly upon excitatory neurotransmitter systems.