Ubiquitinated cytoplasmic inclusions are a characteristic feature of the neuronal pathology of neurodegenerative diseases. Immunocytochemical techniques have identified intermediate filaments associated with ubiquitin-immunoreactive inclusions in Alzheimer's disease (AD), Parkinson's disease (PD), and Pick's disease; however, no core protein has been detected in the ubiquitinated inclusions in amyotrophic lateral sclerosis (ALS). The pathogenesis of these inclusions is not known, but the inclusion may result from an accumulation of an abnormal proteins. Here we report a novel protein of 32.5 kDa detected by polyacrylamide gel electrophoresis, in the spinal cord in ALS patients. A polyclonal antibody raised against this protein and used for Western blotting, suggests that the novel protein is related to actin. Immunocytochemical studies using this antibody indicate that the protein is found in Lewy body-like inclusions in anterior horn cells of ALS, and in Lewy bodies in the substantia nigra in PD.