(Dako, Glostrup, Denmark, diluted 1: 1,000). Sec-tions from which the primary antibodies were omitted served as reaction controls. Antibody binding was visualized with the avidin-biotin-immunoperoxidase complex Vectastain kit (Vector Laboratories, Burlingame, CA, USA) following the manufacturer's protocol; 3, 3'-diaminobenzidine tetrahydrochloride was the chromogen and methyl green, the counterstain. The neuropathological hallmarks in spinal cords of patients with familial ALS are the decreased number of neurons with reactive astrocytosis of the anterior horns and Clarke's nuclei, and degeneration with reactive astrocytosis of pyramidal tracts, posterior columns and spinocerebellar tracts (3-5, 10). Some affected neurons of the anterior horns and Clarke's nuclei have Lewy body-like inclusions, ill-defined irregular structures and cord-like swollen neurites (3-5, 10). Immunoreactivity with the antibody to Cu/ZnSOD1 was readily observed in Lewy body-like inclusions (Fig. 1 a), ill-defined irregular structures (Fig. 1b) and cord-like swollen neurites (Fig. 1c) of the three cases examined. The morphologically intact neurons and the glial components of the spinal cords from the patients with familial ALS as well as those from the normal controls (Fig. 1d) were only very wealky stained or not all. By contrast, the erythrocytes in the specimens examined gave a positive reaction. We also examined the spinal cords for MnSOD2, whose gene is on chromosome 6 (8). As in other neurological disorders previously studied by us (13), MnSOD2 immunoreactivity was observed apparently in cell bodies and proximal processes of reactive astrocytes in the anterior horns (Fig. 1e, f) and degenerated tracts of the ALS patients. Scattered MnSOD2-positive dots (Fig. 1e) in the neuropil were supposed to be localized in the neuroglial cell processes, but we have not yet completely investigated the localization of the dots. The neurons (Fig. 1e) and glial components other than astrocytes of all cases reacted only very weakly or not at all with the antibody