Purpose-To determine the concentration of myocilin in primary open-angle and pseudoexfoliation glaucoma aqueous humor.Methods-Aqueous humor was collected during surgery from patients with primary open-angle glaucoma (POAG), pseudoexfoliation glaucoma (PEXG), and elective cataract removal (control). Volume-equivalent aqueous samples were separated on SDS-PAGE gradient gels. Quantification of myocilin levels was performed using Western blots probed with two independent N-terminal polyclonal anti-myocilin antibodies (AB1 and AB2) followed by densitometry. Myocilin levels in aqueous humor were quantified by plotting the densitometry readings of the aqueous samples against a recombinant myocilin standard curve. Total protein concentration was determined by Bradford protein assay. Transforming growth factor beta 2 (TGFβ2) levels were assessed by ELISA.Results-Myocilin levels are significantly elevated in human POAG aqueous humor when compared to control aqueous humor (AB1: 0.66 ± 0.53 ng/μl vs. 0.23 ± 0.20 ng/μl, p<0.001; AB2: 0.98 ± 0.59 ng/μl vs. 0.65 ± 0.5 ng/μl, p<0.03; mean ± SD). Myocilin makes up a larger percent of the total protein in POAG aqueous humor compared to control aqueous (AB1: 0.26 ± 0.20% vs. 0.10 ± 0.20%, p<0.001; AB2: 0.43 ± 0.32% vs. 0.28 ± 0.18%, p<0.05). In contrast to POAG, myocilin levels were not elevated in PEXG aqueous humor when compared to control aqueous humor. No correlation between myocilin and TGFβ2 levels was observed.Conclusions-Myocilin is elevated in POAG, but not PEXG aqueous humor.