Cholesterol enrichment of the senile plaques was suggested by the positive results obtained with the cholesterol probe filipin and the histoenzymatic method based upon cholesterol oxidase activity. Floating vibratome sections (after formalin fixation) and cryostat (unfixed) sections from human area 22 in 3 cases of stage VI Alzheimer disease were used. Some sections were incubated overnight at 4°C in PBS containing 0.05% filipin complex. Other ones were stained with the cholesterol-oxidase histoenzymatic technique according to the published method: cholesterol was oxidized by cholesterol oxidase, yielding H202 which in presence of peroxidase oxidized in turn Amplex red into resorufin, a highly fluorescent probe. Although not higher in the senile plaque than in the surrounding tissue, the filipin signal faded rapidly in the neuropil and remained strong in the SP. Pan-lipid extraction using chloroform – methanol (1:2 volumes) with concentrated chlorhydric acid 1 % for 18 h at room temperature abolished the signal in the neuropil but the labelling appeared as strong as before in the senile plaque. With the histoenzymatic method, the staining of the plaque remained strong even when cholesterol oxidase was omitted. Resorufin alone was able to stain the plaques. Filipin appears to label hydrophobic material even in the absence of cholesterol; resorufin – i.e. oxidized amplex red – labels amyloid in the absence of any cholesterol oxidase activity. Other techniques than filipin and cholesterol oxidase are required to prove the presence of cholesterol in the senile plaques.