Purpose: To investigate the role of oxidative stress and lipid peroxidation in the pathogenesis of primary open-angle glaucoma (POAG). Materials and methods: The activities of myeloperoxidase (MPO), catalase (CAT), and the levels of plasma malondialdehyde (MDA) were measured in 40 (15 men and 25 women) patients with POAG and 60 (30 men and 30 women) healthy controls. Results: There was no significant difference in the activities of CAT and MPO between the POAG patients and the controls. However, the plasma MDA level was significantly higher in patients than the controls. Conclusion: The results of this preliminary study suggest that the possible alterations of plasma MDA levels may be associated with the pathogenesis of POAG, but further research is needed to understand the role of oxidative damage in this important disorder of aging. © 2005 Nature Publishing Group All rights reserved.