OBJECTIVES: Study the oxidative status in patients with primary open-angle glaucoma (POAG) in order to evaluate if antioxidant supplementation may benefit these patients. METHODS: Enzimatic-colorimetric biochemical assays for determining peroxidative (malondialdehyde, MDA), antioxidant (total antioxidan statust TAS) and nitrosative (nitric oxide, NO) activities were carried out in the aqueous humour from one hundred and twenty patients operated alternatively for primary open angle glaucoma (POAG-G) or cataracts (CAT-G). A comparison between groups was done by using the Student T test by means of the SPSS statistical package. RESULTS: The MDA levels were significantly higher (p<0.001) in the aqueous humour from the POAG-G than in the CAT-G. The TAS levels were significantly lower (p<0.01) in the POAG-G samples than in the comparative ones. NO levels were significantly higher (p<0.05) in the POAG-G samples than in the CAT-C. CONCLUSION: The relationship between pro-oxidant and antioxidant activities in the aqueous humour was strongly dysbalanced towards oxidative capacity in the glaucoma patients. All data suggest that oxidative stress has to be considered among the etiopathogenical mechanisms of advanced glaucoma. The possibility remains that antioxidant supplementation may benefit the glaucoma cases displaying lower antioxidant capacity in the described laboratory tests.