Proton magnetic resonance spectroscopy (MRS) allows accurate and noninvasive biochemical assay of living tissues. In vivo measurements provided by MRS have greatly enhanced our understanding of the pathophysiology of dementia. Increases in choline and myo-inositol (markers of membrane turnover) have been demonstrated in several studies on patients with Alzheimer's disease (AD), suggesting the presence of a significant cellular membrane (and glial) pathology in this disorder. Large decreases in brain N-acetylaspartate (NAA) (a marker of neuroaxonal integrity) are commonly seen in AD as well as in other forms of dementia in cerebral gray and white matter, indicating the presence of significant axonal damage. Since greater NAA decreases have been demonstrated in brains of patients with clinically more severe disease, NAA could provide an index relevant to patients' clinical status. Brain metabolic changes can be independent of abnormalities detected by conventional magnetic resonance imaging (MRI), since proton MRS may show a normal metabolic pattern in patients with mild neurological impairment and severe MRI abnormalities. However, quantitative measurements of regional brain volumes can be useful in the diagnosis of dementia. Thus, proton MRS, alone or combined with new quantitative magnetic resonance techniques, can provide sensitive indices able to monitor disease progresson or effects of drug therapy.