To determine the concentration of myocilin in primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PEXG) aqueous humor.Aqueous humor was collected during surgery from patients with POAG, PEXG, and elective cataract removal (control). Volume-equivalent aqueous samples were separated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gradient gels. Quantification of myocilin levels was performed using Western blots probed with 2 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 β 2 levels were assessed by enzyme-linked immunosorbent assay.Myocilin levels are significantly elevated in human POAG aqueous humor when compared with 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 with 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 with control aqueous humor. No correlation between myocilin and transforming growth factor β 2 levels was observed.Myocilin is elevated in POAG, but not in PEXG aqueous humor.