A total of 151 patients with open-angle glaucoma, 23 ones with closed angle glaucoma, and 57 ones with age-associated cataracts were examined. The reference group consisted of 21 subjects with posttraumatic cataracts (1.5 years after the injury) and normal subjects. Nonprotein sulfhydryl groups (glutathione) were measured in the peripheral blood, aqueous humor, and in tissue samples from the scleral drainage sites, obtained in antiglaucoma surgery and in surgery for cataract extraction. Aqueous humor of patients with posttraumatic cataracts, blood samples of these patients and normal subjects were examined for control. The level of sulfhydryl groups was found significantly lowered in the anterior chamber humor of patients with open-angle glaucoma, particularly in those with disease Stages II and III as against the controls. The content of sulfhydryl groups was lowered in the tissue samples from the scleral drainage area of patients with open-angle glaucoma Stages II and III vs. that in the patients with Stage I condition. Similar changes were found in the red cells of patients with Stages II and III open-angle glaucoma. Glutathione is an important component of the cellular antioxidant system. The findings point to a reduction of the processes of antioxidant defense of ocular tissues, developing as early as in the first stage of open-angle glaucoma. Lipoic acid administration for 2 months was associated with a rise of glutathione level in the red cells of patients with Stages II and III open-angle glaucoma.