The amount of plaque material derived from the sheaths of the elastic-like fibers in the cribriform layer of the trabecular meshwork (sheath-derived or SD plaques) was quantitatively evaluated in normal eyes and in trabeculectomy specimens of chronic simple, intermittent angle closure, and pseudoexfoliation glaucoma. The amount of SD plaque material increases with age but no correlation between age and SD plaques was found in any of the glaucomas evaluated. In comparison to normal eyes, the amount of SD plaque material was significantly greater in cases of chronic simple glaucoma and in cases of intermittent narrow angle glaucoma, but not in pseudoexfoliation glaucoma. In the latter, number and distribution of SD plaques resembled those of normal eyes. SD plaques were also found in the outer wall of Schlemm's canal. In normal eyes there was a correlation between outer-wall plaques and age as well as between inner- and outer-wall plaques. These correlations were not found in the different types of glaucoma. Our findings indicate that in addition to the age-related increase in plaque material, there is in glaucomatous eyes some plaque material which is distributed unevenly in the inner- and outer-wall of Schlemm's canal. This additional material was not found in pseudoexfoliation glaucoma, indicating that elevated intraocular pressure alone can not be responsible for plaque formation.