The Lewy body is an intraneuronal inclusion body that is one of the histologic hallmarks of Parkinson's disease, a degenerative disease of the brain. Ultrastructural analysis has shown that the Lewy body is composed of straight 7-20 nm filaments and amorphous elements. Previous light microscopic, immunocytochemical studies have suggested the presence of neurofilament, microtubule, ubiquitin, and paired helical filament-related epitopes in Lewy bodies. Yet the biochemical composition of the Lewy body remains incompletely elucidated. The ultrastructural and immunocytochemical similarities and differences between the Lewy body and the neurofibrillary tangle of Alzheimer's disease raise questions as to their relation to each other and possible shared mechanisms of formation. In this study the authors examine whether ultrastructural immunocytochemical analysis of Lewy bodies confirms the light microscopic data, whether the structures and epitopes of Lewy bodies share with Alzheimer's disease neurofibrillary tangles the property of insolubility in sodium dodecyl sulfate, and speculate about the subunit composition of Lewy body filaments.