PURPOSE. To assess the level of plasma glutathione in patients with untreated primary open-angle glaucoma. METHODS. Twenty-one patients with newly diagnosed primary open-angle glaucoma and 34 age-and gender-matched control subjects were subjected to a blood analysis to detect the level of circulating glutathione in its reduced and oxidized forms. The effect of age, gender, and systemic blood pressure on circulating glutathione levels was also analyzed. RESULTS. Age had a negative effect on the level of both reduced and total glutathione (P=0.002, r=- 0.52 and P=0.002, r=- 0.52, respectively) in control subjects but not in patients with glaucoma (P>0.05, r=0.27, and P>0.05, r=0.22, respectively). In the control group, men demonstrated higher levels of both reduced and total glutathione than did women (P=0.024 and P=0.032, respectively). After correction for age and gender influences on blood glutathione levels, patients with glaucoma exhibited significantly lower levels of reduced and total glutathione than did control subjects (P=0.010, F=7.24 and P=0.006, F=8.38, respectively). No differences between study groups were observed in either oxidized glutathione levels or redox index (P > 0.05, F=0.50; and P > 0.05, F=0.30, respectively). CONCLUSIONS. Patients with glaucoma exhibit low levels of circulating glutathione, suggesting a general compromise of the antioxidative defense. PURPOSE. To assess the level of plasma glutathione in patients with untreated primary open-angle glaucoma. METHODS. Twenty-one patients with newly diagnosed primary open-angle glaucoma and 34 age-and gender-matched control subjects were subjected to a blood analysis to detect the level of circulating glutathione in its reduced and oxidized forms. The effect of age, gender, and systemic blood pressure on circulating glutathione levels was also analyzed. RESULTS. Age had a negative effect on the level of both reduced and total glutathione (P = 0.002, r = - 0.52 and P = 0.002, r = - 0.52, respectively) in control subjects but not in patients with glaucoma (P> 0.05, r = 0.27, and P> 0.05, r = the control group, men demonstrated higher levels of both reduced and total glutathione than did women (P = 0.024 and P = 0.032, respectively). After correction for age and gender influences on blood glutathione levels, patients with glaucoma exhibited significantly lower levels of reduced and t No differences between study groups were observed in either oxidized glutathione levels or redox index (P> 0.05, F = 0.50; respectively) and P> 0.05, F = 0.30, respectively). CONCLUSIONS. Patients with glaucoma exhibit low levels of circulating glutathione, suggesting a general compromise of the antioxidative defense.