We used light and electron microscopy to compare ten specimens of anterior chamber angle tissue obtained by trabeculectomy from seven patients with juvenile glaucoma (primary glaucoma with open iridocorneal angle in young humans with specimens of normal trabecular meshwork from humans of the same ages. In all cases of juvenile glaucoma, we observed a thick compact tissue consisting of cells with fine processes and extracellular substances at the anterior chamber side of Schlemm's canal and abnormal deposits of ground substances in the thick tissue. These observations strongly suggest that the thick compact tissue represents an immature development of the trabecular meshwork and may be one of the primary causes of increased intraocular pressure in juvenile glaucoma. Our studies indicate that both congenital and juvenile glaucoma occur because of developmental immaturity of the trabecular meshwork in anterior chamber angle tissue and that the more extensive the immaturity, the earlier the glaucoma will become manifest.