Several parameters indicators of oxidative stress were evaluated in blood from individuals with the sporadic form of amyotrophic lateral sclerosis (SALS) and compared to healthy controls. Plasma levels of 2-thiobarbituric-reactive substances (TBARS), products of lipid peroxidation, were significantly higher (p < 0.03) in the SALS patients compared to controls. The concentration of plasma antioxidants (alpha-tocopherol, beta-carotene, ubiquinol-10 and glutathione) and the activity of red blood cell CuZn superoxide dismutase were not significantly different between the groups. The ratio TBARS/alpha-tocopherol was 47% higher in the SALS individuals than in controls. Protein thiols and protein-associated carbonyls in red blood cell membranes and supernates were similar for both groups. A positive correlation (r2 = 0.91) was found between the concentration of protein-associated carbonyls in red blood cells and the onset of clinical symptoms. These findings are in agreement with several reports showing higher levels of oxidative damage to cell components in ALS.