Increased generation of reactive oxygen species may underlie the pathophysiology of Friedreich ataxia (FRDA). The authors measured concentrations of 8-hydroxy-2'-deoxyguanosine (8OH2'dG), a marker of oxidative DNA damage, in urine and of dihydroxybenzoic acid (DHBA), a marker of hydroxyl radical attack, in plasma of 33 patients with FRDA. They found a 2.6-fold increase in normalized urinary 8OH2'dG but no change in plasma DHBA as compared with controls. Oral treatment with 5 mg/kg/day of the antioxidant idebenone for 8 weeks significantly decreased urinary 8OH2'dG concentrations, indicating that 8OH2'dG may be useful in monitoring therapeutic interventions in patients with FRDA.-1721