In eight patients with chronic open-angle glaucoma and associated trabecular pigmentation, trabeculectomy and peripheral iridectomy specimens were studied by light and electron microscopy. Clinically, three patients displayed signs of classic pigmentary glaucoma (Group 1). In the other cases chronic open-angle glaucoma was associated with varying degrees of expression of the full pigmentary glaucoma syndrome (Group 2). Histopathologic examination of peripheral iridectomy and trabeculectomy specimens from Group 1 showed: (1) marked focal atrophy and hypopigmentation of iris pigmented epithelium with an apparent delay in melanogenesis. The dilator muscle was thickened except for occasional thinned areas. (2) The trabeculectomy specimens revealed excessive amounts of pigmented epithelial melanosomes and moderate accumulation of electron-dense basement membrane-like material in the juxtacanalicular meshwork. Similar specimens from Group 2 showed: (1) minimal hypopigmentation of the iris pigmented epithelium with normal melanogenesis. The iris stroma and dilator muscle were normal. (2) Trabeculectomy specimens displayed excessive electron-dense basement membrane-like material in the juxtacanalicular meshwork and minimal to moderate accumulation of melanosomes.