In a group of 331 sporadic amyotrophic lateral sclerosis (ALS) cases, we identified a new Cu/Zn superoxide dismutase single base substitution, N19S, in two patients. In the first case, seven healthy family members of 15 carried the substitution. Controls (n = 268) and familial ALS index cases (n = 180) were screened and one control subject with N19S was identified. Our data show that, despite a possible role of susceptibility factor for ALS, N19S alone cannot be considered as a direct cause for the disease.