A role mutations in the superoxide dismutase (SOD)-1 gene in the pathogenesis of amyotrophic lateral sclerosis (ALS) has been discussed. To investigate immunohistochemical alterations of SOD in the spinal cord affected with the disease, we examined 3 patients with SOD1 mutation-associated family with ALS, 20 patients with sporadic ALS and 10 control individuals. Lewy body-like hyaline inclusions (LBHIs) were seen in the anterior horn cells of all the familial patients and 10 of the 20 sporadic patients, while skein-like inclusions (SIs) and Bunina bodies (BBs) were present in the 20 sporadic patients but not in the familial patients. The primary antibodies used for immunostaining were rabbit antisera raised against human SOD1 and SOD2. The anti-SOD1 antibody reacted strongly with all LBHIs of each familial patient and with some LBHIs of each sporadic patient. The cytoplasm of morphologically intact and degenerated spinal cord neurons as well as spheroids seen in the cases examined was only weakly stained by the antibody to SOD1 or not at all. The reactive astrocytes displayed weak to moderate staining for SOD1. The anti-SOD2 antibody strongly immunolabeled the reactive astrocytes and microglia. LBHIs of both familial and sporadic ALS were negatively stained for SOD2. Spinal cord neurons and spheroids of each case exhibited no significant SOD2 immunoreactivity. Neither antibodies reacted with SIs nor BBs. These results indicate that SOD1 may be involved in the formative process of LBHIs especially in familial ALS but not always in that of SIs or BBs, and imply that SOD2 may have no connection with any of these ALS-related abnormal structures.