Abstract Brain sections from Alzheimer's disease (AD) patients and controls were treated with basic fibroblast growth factor (bFGF) and then immunostained with anti-bFGF. Additional sections were treated with biotinylated bFGF without using the anti-bFGF. Labelling was visualized by the ABC method. Both protocols above intensely labelled neurofibrillary tangles, senile plaques and amyloidotic vessels in AD brains. Omission of the bFGF treatment abolished the staining of the AD lesions. The pretreatment of sections with heparitinase also reduced their staining. These results indicate that AD lesions contain bFGF-binding sites and that the chemical substrate for bFGF binding to AD lesions was heparan sulfate.