Motor neurons from the brain stems of amyotrophic lateral sclerosis (ALS) and control patients were examined with immunoantibodies to CuZn-superoxide dismutase (CuZnSOD) and Mn-superoxide dismutase (MnSOD). We found that there was a marked staining for CuZnSOD in all the motor nuclei, the hypoglossus, ambiguus, facialis and trigeminus from the ALS patients, but not in the controls. The same neurons from the ALS patients also stained very intensely for MnSOD, whereas the neurons from the control patients stained weakly or not at all. Loss of neurons was also a very consistent finding and was noted in all the motor nuclei from the ALS patients. There was a proliferation of glial cells which stained strongly both for CuZnSOD and for MnSOD accompanying the loss of the neurons. These results indicated that there was an apparent increase of superoxide dismutase immunoreactivity in motor neurons of ALS patients. We conclude that CuZnSOD and MnSOD immunoreactivity is increased in motor neurons and glia in the brain stems of patients with ALS, specific for the terminal phase of this disease.