We studied the number of large-sized neurons and neurofibrillary tangles (NFT) in the tuberomammillary nucleus (TM) of the hypothalamus from cases with Alzheimer's disease (AD) and age-matched controls. Numerous NFT were found in TM of AD. However, NFT was never observed in this nucleus of age-matched controls. The number of large-sized neurons was significantly reduced in AD compared with that in controls. Since the majority of large neurons in TM appear to correspond to histamine neurons, the loss of large neurons observed in TM may, at least partly, cause the histaminergic dysfunction in AD brain.