To determine the possible role of Cu/Zn superoxide dismutase (SOD1) in the pathophysiology of sporadic amyotrophic lateral sclerosis (SALS), we measured SOD1 activity in red blood cell lysates in patients with SALS. SOD1 activity in red blood cell lysates was independent of age and sex in control patients, and no significant difference was found between the levels of SOD1 activity in controls (1174.8 +/- 213, n = 29) and SALS patients (1203.4 +/- 214, n = 27). These results suggest that point mutations in the SOD1 gene are apparently unrelated to SALS.