The pathogenesis of amyotrophic lateral sclerosis is poorly understood. In one or two percentage of patients, mutations in the SOD1 gene are known to underly the disease. Even in these cases, the mechanism of cell death remains unclear. Most researchers agree that damage by reactive oxygen species is involved in this process, but whether the latter plays a primary role or is an epiphenomenon is uncertain. As evidence for oxidative stress is not only found in mutant SOD1-related familial amyotrophic lateral sclerosis, but also in sporadic amyotrophic lateral sclerosis, it is tempting to speculate that a similar mechanism is at work in both forms of the disease.