The effect of piracetam (a putative enhancer of cerebral metabolism) on regional CMRGlu was studied by positron emission tomography of 2[18F]-fluoro-2-deoxy-D-glucose in nine patients with Alzheimer's disease, and in seven cases with multiinfarct dementia or unclassified dementia. In Alzheimer's disease, i.v. administration of piracetam, 6 g b.i.d. for 2 weeks, significantly improved rCMRGlu in most cortical areas, whereas no effect on CMRGlu of the drug was observed in the multiinfarct dementia/unclassified dementia groups. These results lend further support to the notion that adjuvant piracetam treatment is of benefit in Alzheimer's disease. They may also indicate that the typical metabolic depression in Alzheimer's disease is caused by complex interaction of disturbed transmitter and cellular function rather than by a specific deficit in the cholinergic system alone.