The greatest bulk of aqueous passes through a sieve-like trabecular wall to reach Schlemm's canal. The vacuoles of the endothelial lining of the trabecular wall are pressure-dependent one-way valves, adapted morphologically to provide for adequate aqueous transfer. Resistance to aqueous outflow seems to be most concentrated in the juxtacanalicular tissue which is also the site of the greatest mucopolysaccharide concentration and phagocytic activity. Normal intraocular pressure may be maintained through a balance between hydrophilic polymerized MPS and hydrophobic depolymerized MPS. It may be effected also by a phagocyte-induced, self-cleaning biologic filter mechanism of the trabecular wall. The use of electron microscopy and improved biochemical techniques have led recently to a greater understanding of the anatomy of the structures concerned with the outflow of aqueous from the anterior chamber. Despite these advances, no clear-cut differences between normal and glaucomatous eyes have emerged thus far. However, the future should bring more knolwedge as the stimulus of conflicting theories leads to progress.