Two antigens, G7 and G9, which are labelled by monoclonal antibodies in Lewy bodies in brains from patients with Parkinson's disease, were characterized by two-dimensional electrophoresis, followed by electroblotting, in order to explore their possible relationship with neuronal degeneration in this disease. The G7 antigen was found in the substantia nigra of subjects with Parkinson's disease and progressive supranuclear palsy, as well as in normal subjects. It was also found in the dopaminergic nucleus paranigralis and the locus coeruleus. The G9 antigen was found in the substantia nigra and locus coeruleus, but also in the caudate nucleus, terminal region of the nigrostriatal dopaminergic neurons, and in the cortex and cerebellum, terminal regions of the noradrenergic neurons in the locus coeruleus. The identity of the antigens remains unknown. They do not correspond to tyrosine hydroxylase or neurofilaments previously detected in Lewy bodies, or to other cytoskeletal proteins. Nor are they related to the presence of neuromelanin in the cells that degenerate in Parkinson's disease. The proteins, or at least the epitopes labelled by the antibodies, are found in normal brain, suggesting that these proteins do not play a causal role in the formation of the Lewy bodies in degenerating neurons in Parkinson's disease. The G7 antigen is absent from the cholinergic substantia innominata, where Lewy bodies are also found, indicating that these antigens are not essential for the formation of the corpuscle.