Alpha-synuclein has been implicated in neurodegenerative diseases characterized by Lewy bodies. However, we have only scanty information on the immunoreactivity of alpha-synuclein in other inclusion bodies such as the Lewy body-like inclusions and the skein-like inclusions observed in motor neuron disease (MND). In this report, we immunocytochemically investigated inclusion bodies observed in the anterior horn neurons of the spinal cord in 29 patients with sporadic MND. Sixteen age-matched patients without any neurological disease served as controls. In MND patients, we recognized Lewy body-like hyaline inclusions, skein-like inclusions, Bunina bodies, basophilic inclusions, and intracytoplasmic hyaline (colloid) inclusions, but none of them were immunostained for alpha-synuclein. Our findings in this study do not support the hypothesis that MND could be classified as one of the diseases grouped as alpha-synucleinopathies.