The diagnostic significance of tau proteins in cerebrospinal fluids (CSF) has been described in many cases of dementia of Alzheimer type (AD). However, in patients with other diseases showing neurofibrillary tangles (NFT) similar to those in AD, tau proteins in cerebrospinal fluids have not been rigorously investigated. In particular, differentiating corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP) is clinically and pathologically difficult, and a useful biochemical marker to discriminate these two diseases has been a subjects of clinical interest. Therefore, we examined the usefulness of CSF tau and amyloid beta (A beta) proteins for the differentiation between CBD and PSP. CSF total tau (t-tau) and A beta proteins were measured with the sandwich ELISA method (Innogenetics, Belgium). CSF tau protein phosphorylated at serine 199 (p-tau) was measured by a recent established sandwich ELISA (Mitsubishi Chemical Co.). In conclusion, measurement of tau protein levels in CSF may be useful for the differential diagnosis of CBD from PSP. We also suggest that CSF p-tau may be a better biochemical marker than CSF t-tau.