We investigated through a population-based case-control study the hypothesis that disturbances in the chemistry of copper and zinc and in activity of the antioxidant enzyme copper/zinc superoxide-dismutase (SOD1) are involved in the etiopathogenesis of sporadic amyotrophic lateral sclerosis (ALS). We recruited 20 patients with sporadic ALS and 22 population controls from three northern Italian provinces, and we analyzed zinc and copper content and SOD1 activity in erythrocytes. These variables were unrelated to disease progression as evaluated through a disability score; zinc concentrations inversely correlated with copper in referents but not in patients. SOD1 activity was lower and erythrocyte zinc and copper levels were slightly higher in patients than in referents. Comparing the second to the bottom tertile of erythrocyte SOD1 activity, relative risk of ALS was 0.4 (95% confidence interval 0.1-2.0); the risk further decreased to 0.1 (95% confidence interval 0-0.9) for comparison of highest to lowest tertile (P for trend 0.027). Copper and zinc levels were not associated with disease risk. Our findings indicate that a lower SOD1 activity is associated with ALS, but we cannot be sure whether this association is a marker of causal action or is secondary to a confounder, or to disease onset itself.