A quantitative investigation was performed on the large neurons in the neostriatum and basal nucleus of Meynert (bnM) in patients with Alzheimer's disease (AD) and progressive supranuclear palsy (PSP). The degree of decrease of the large neurons in the neostriatum was quite similar to that in the bnM; these decreases were significantly correlative in AD, but not in PSP. These findings indicate that the large neurons in the neostriatum and bnM, which are considered to be cholinergic and to exclusively possess nerve growth factor receptors in the cerebrum, degenerate simultaneously in an equal ratio in AD.