The extracellular matrix protein heparin sulfate proteoglycans (HSPG) has been found in the neurofibrillary pathology of Alzheimer disease. This study was performed to determine if similar proteoglycans might be present in the fibrillary inclusions of other neurodegenerative diseases. Basic fibroblast growth factor (bFGF) binding to heparinase sensitive sites was used as an assay for HSPGs. We found that the inclusions of Pick and Parkinson diseases as well as progressive supranuclear palsy contained heparinase sensitive bFGF binding sites while the inclusions of diffuse Lewy body disease lacked bFGF binding sites. These findings indicate that HSPG's interactions and possible role in the formation of intraneuronal inclusions are not limited to Alzheimer disease.