AIM: To assess the role of the immune system in the pathophysiology of normal tension glaucoma (NTG) by analyzing the level difference of the cytokine interleukin-6 (IL-6) and IL-12 in peripheral blood between patients with NTG and cataract.·METHODS: The concentrations of IL-6, IL-12 were assessed in 37 cases of NTG patients, 40 cases of cataract patients by Enzyme-Linked immunosorbent assay, 3mL peripheral blood was extracted separately to do the test. No significant differences existed in age or gender between the two groups.·RESULTS:IL-6, IL-12 concentrations in NTG group and cataract group were (1.402±2.297)pg/mL, (8.214±5.355)pg/mL and (12.475±3.973) pg/mL, (20.116±4.216) pg/mL respectively. The mean concentrations of IL-6 and IL-12 in NTG group were significantly lower than these in cataract group (P<0.05).·CONCLUSION: The levels of IL-6, IL-12 in peripheral blood of patients with NTG were lower than those of cataract group. The alteration of the cellular immune system in patients with NTG supports our hypothesis that the immune system may play an important role in the initiation and sustainment of glaucomatous optic neuropathy.