GUAM is one of three endemic foci whose indigenous (Chamorro) people have an unusually high incidence of fatal neurodegenerative disorders, amyotrophic lateral sclerosis (ALS) and Parkinsonism—dementia (PD). Recently, mutations in the Cu/Zn superoxide dismutase (SOD-1) gene have been identified in some familial cases of ALS. To investigate if mutations in the SOD-1 gene are also involved in the pathogenesis of ALS and PD of Guam, we analyzed the SOD-1 gene in Chamorros. No mutations were found in Chamorros with ALS or PD, indicating that mutations in the SOD-1 gene do not underlie the high-incidence neurodegenerative disorders of Guam.