['To test the hypothesis that immune activation occurs in glaucoma by comparing concentrations of multiple cytokines in aqueous humor (AH) from patients with primary open angle glaucoma (POAG) and from cataract patients without glaucoma as controls.', 'Cytokine concentrations in AH obtained during surgery were measured using microparticle-based immunoassays. Localized expression of IL-8 protein was investigated by immunohistochemistry of human eyes.', 'Eight cytokines (IL-1β, IL-2, IL-4, IL-5, IL-10, IL-12, IFN-γ, and TNF-α) were below the limits of detection, and two cytokines (IL-18 and IL-15) were detected at low levels or in only a few patients. Although IL-6 was detected in 26 of 30 control patients (median, 2.7 pg/mL) and in 23 of 29 POAG patients (median, 1.6 pg/mL), the difference was not statistically significant. IL-8 was detected in 28 of 30 control patients (median, 1.8 pg/mL) and in all 29 POAG patients (median, 4.9 pg/mL). The higher IL-8 concentration in the AH of POAG patients was statistically significant (P < 0.001). In pairs of eyes from patients with asymmetric glaucomatous optic nerve damage, IL-8 concentration was higher in the AH of the more severely affected eye (P < 0.05). Patients with severe visual field defects had higher IL-8 concentrations in the AH than did patients with mild visual field defects. IL-8 protein expression was found in human retina and optic nerve.'] Does multiplex cytokine analysis reveal elevated concentration of interleukin-8 in glaucomatous aqueous humor?