Senile dementia of Lewy body type or Lewy body dementia (LBD), characterized neuropathologically by the presence of Lewy bodies in the brainstem and cortex, and in most cases neocortical senile plaques (but few or no tangles), bears a closer resemblance to Parkinson's (PD) than to Alzheimer disease (AD) in its cholinergic neurochemical pathology. Thus, reductions in the biochemical activity of choline acetyltransferase were generally more extensive in neo- as opposed to archicortical regions in LBD (especially hallucinating cases) and in PD, whereas muscarinic receptor binding was significantly increased in LBD and PD but not in AD. Nerve growth factor receptor (P75) assessed immunocytochemically in the archicortex were decreased in PD and, to a lesser extent, in LBD in conjunction with reductions of neuronal numbers in the nucleus of Meynert (Ch4), but were relatively spared in AD. These observations indicate that although AD is primarily associated with dysfunction of cholinergic axonal input to the cortex, LBD and PD are more likely to involve degeneration of the basal forebrain cholinergic system. Relevance of the findings in terms of aetiopathology and cholinergic treatment strategies is discussed.