Oxidative stress has been reported to increase with aging; however, the scientific evidence is controversial. We therefore aimed to analyze the relationship between aging and some markers of oxidative stress. A cross-sectional and comparative study was carried out in a sample of 249 healthy subjects: (i) 25-29 years (n = 22); (ii) 30-39 years (24); (iii) 40-49 years (30); (iv) 50-59 years (48); (v) 60-69 years (60), and (vi) >or= 70 years (65). We measured lipoperoxides and total antioxidant status in plasma and superoxide dismutase and glutathione peroxidase activities in erythrocytes. There was an age-related increase in lipoperoxides, which was evident in the comparison of the group of 25-29 years (0.22 0.11 micromol/l) with the group of 60-69 years (0.38 +/- 0.18 micromol/l, p < 0.01) and >or= 70 years (0.42 +/- 0.19, p < 0.001). Conversely, the total antioxidant status showed an age-related decrease (25-29 years, 1.4 +/- 0.31 mmol/l vs 60-69 years, 1.1 +/- 0.21 and >or= 70 years, 1.1 +/- 0.22, p < 0.05 for each). In erythrocytes, glutathione peroxidase activity showed an age-related decrease (25-29 years, 7,966 +/- 1,813 UI/l vs 60-69 years, 6,193 +/- 2,235 and >or= 70 years, 6,547 +/- 2,307, p < 0.001 for each), whereas superoxide dismutase activity was similar in all age groups. Importantly, there was no age-related change in oxidative stress markers in subjects of < 60 years. These findings suggest that age of >or= 60 years may be associated with increased oxidative stress.