Immunohistochemistry (IHC) and ultrastructural study were performed on 19 demented autopsy cases of sporadic Alzheimer's disease (AD). Semiquantitative IHC assessment of the pathological changes, according to the criteria of the Consortium to Establish a Registry of Alzheimer's Disease (CERAD) and the Consortium on Dementia with Lewy Bodies, showed morphological hallmarks of AD in 18 demented patients. It was found that 11 of these cases fulfilled criteria for "pure" AD, whereas the remaining 7 cases, with mixed findings, Lewy bodies (LBs) and Lewy-related dystrophic neurites, neuritic plaques (NP) and sometimes neurofibrillary tangles (NFT), met the criteria for Lewy body variant of Alzheimer's disease (LBV). One case with brain stem and cortical LBs but without NP and NFT was finally diagnosed as a pure form of dementia with Lewy bodies (DLB). Regional distribution and semiquantitative assessment frequency of alpha-synuclein-immunoreactive LBs, tau-immunoreactive NFT and beta-amyloid immunoreactive senile plaques, were compared between LBVand AD. Ultrastructural examination confirmed the filamental structure of cortical LBs. In conclusion, IHC study including antibody to alpha-synuclein, the sensitive marker for Lewy bodies, revealed the coexistence of brain stem and cortical LBs and pathological features of AD in a great part of dementia cases. Patients with mixed, LBs, NP and sometimes NFT pathology, fulfilled neuropathological CERAD criteria for LBV. Semiquantitative comparative IHC study, according to LBs- and NFT-scores and CERAD NP-scores showed in the LBV group a significantly lower frequency of NFT coexisting with neocortical LBs than in the group with pure form of AD.