We compared samples of different brain areas from patients with Alzheimer's disease (AD), progressive supranuclear palsy (PSP), controls subjects and from 4 patients who met the clinical and pathological criteria for frontotemporal dementia (FTD), using a Western blot analysis. We used polyclonal antibodies directed against Tau proteins and the monoclonal antibody AD2 for the immunodetection of the pathological Tau proteins which are the basic components of neurofibrillary degeneration. In the PSP and AD cases, we respectively detected the abnormal Tau proteins 64 and 69 and the Tau proteins 55, 64, and 69, systematically associated with bands and smears, corresponding to catabolic products or aggregates of these abnormal Tau proteins. In FTD cases, the abnormal Tau proteins 55, 64 and 69 were also detected in the frontal and temporal poles from the autopsied case and in the cortical biopsies. However, the profiles were different because smears and proteolytics products of Tau proteins were absent. There was no detection of abnormal Tau proteins in control brain homogenates and in biopsies from patients with other neurodegenerative disorders such as spongiform encephalopathies or primitive gliosis. These results demonstrate that pathological Tau proteins are produced during FTD degenerating process, despite the absence of neurofibrillary lesions.