In order to evaluate the quantitative changes in the neostriatum in progressive supranuclear palsy (PSP), sections of the caudate head (CN) and putamen (PT) from 4 PSP patients were stained with Klüver-Barrera, and the cell body and nuclear area of the neurons were measured by a digitizer. Obtained results were compared to those of 6 age-matched control and 4 Alzheimer's disease and senile dementia of Alzheimer type (AD/SDAT) subjects which were previously reported. The number of large neurons (nuclear area greater than 101 microns 2) in PSP was about 40% (P less than 0.01) and 30% (P less than 0.01) of that of the controls in CN and PT, respectively. In contrast, the number of small neurons in PSP (nuclear area less than 100 microns 2) was well preserved. The values were quite similar to those in AD/SDAT. The implications and possible significance are discussed.