Cholinesterase (ChE) inhibitors improve or stabilize cognitive impairment in patients with Alzheimer disease (AD). However, the regional metabolic and perfusion correlates of treatment with ChE inhibitors are not fully known. Twenty-four patients with mild to moderate AD were evaluated with Tc-ethyl cysteinate dimer (ECD) single-photon-emission CT scanning (SPECT), before and after 4.3 +/- 1.1 months of treatment with ChE inhibitors (donepezil, rivastigmine). Clinical evaluations included the Mini-Mental State Examination (MMSE) as well as the Neuropsychiatric Inventory (NPI). Inclusion criterion was a clear favorable response to therapy with ChE inhibitors (MMSE improvement of at least 2 points; total NPI improvement of at least 4 points). SPECT data were analyzed by Statistical Parametric Mapping (SPM 99, Wellcome, Department of Cognitive Neurology, London, UK). SPM analysis showed a significant increase (P < 0.01) of regional cerebral perfusion (rCBF) after short-term ChE inhibitor therapy with respect to baseline in the right anterior cingulate, the dorsolateral prefrontal, and the temporoparietal areas bilaterally. These data suggest that cognitive or behavioral benefits after ChE inhibitor therapy are related to a clear increase of rCBF in crucial areas specifically involved in the attentional and limbic networks.