Using a sensitive sandwich enzyme-linked immunosorbent assay (ELISA) method, we measured the concentration of total tau protein in the cerebrospinal fluid (CSF) from nine patients with corticobasal degeneration (CBD) in comparison with 12 normal control subjects in order to assess its diagnostic value. The CSF concentration of tau in patients with CBD (0.69, 0.20 ng/ml; mean, SD) was higher than that in, the normal controls (0.48, 0.14 ng/ml, P = 0.0076 unpaired t test). This increase in CBD patients may reflect widespread tau pathology in CBD, but should be interpreted with reserve as an aid to diagnosis.