Abstract: The nucleus of Meynert belongs to cholinergic system and its damage is thought to contribute to dementia. The present report dealt with the nucleus basalis of Meynert quantitatively, with age-matched contrils, in patients wieh the following disases, multiisystem degeneration, hallervorden-spatz, idiopatic par kinsonim, parkinsonism and amyotrophic lateral sclerosis. No change of the nucleus was observed in all these in all these cases except for the multi-system degeneration in whick there was marked reduction of neurons.