The content of nitrite (final metabolite of nitroradical) was measured in aqueous humor of patients with glaucoma and cataract. The level of NO formation is increased at the initial stage of glaucoma and decreases with the disease progress. A direct correlation between the level of nitrite in aqueous humor and coefficient of easiness of its discharge was detected. Cataract is associated with a high level of nitrite in intraocular fluid. The results are discussed from the viewpoint of ocular hydro--and hemodynamic regulation and NO involvement in the free radical oxidation reactions, playing an important role in the pathogenesis of both diseases.