The straight fibrils of the Lewy body contain an epitope related to phosphorylation of the KSPV motif common to the C termini of the 200- and 170-kDa neurofilament subunits and tau. To further characterize this phosphorylated neurofilament/tau epitope in Lewy bodies and to analyze the constituents of isolated Lewy bodies we used a combined biochemical and immunochemical approach. In formalin-fixed paraffin-embedded tissue cortical Lewy bodies were labelled by monoclonal antibodies directed to phosphorylation-dependent KSPV epitopes in the sequences of neurofilament and phosphorylation-independent epitopes. Immunoblotting of solubilized Lewy body fibrils with the same antibodies which stained Lewy bodies in tissue sections revealed that the immunoreactive Lewy body proteins were phosphorylated neurofilament subunits. An antibody to the 68-kDa neurofilament subunit labelled Lewy bodies and Lewy body protein at 50-68 kDa. We conclude that the shared phosphorylated epitope in Lewy body fibrils and paired helical filaments is related to the common KSPV sequence in neurofilament and tau, and that all three neurofilament subunits are present in the Lewy body. This result indicates that although Lewy bodies and neurofibrillary tangles share epitopes they are comprised of distinct structural subunits.