Unilateral glaucomatous optic neuropathy and optic nerve transections were produced in cynomolgus monkeys, and the optic nerve heads were examined by light and electron microscopic immunohistochemistry. Glaucomatous nerve heads showed increased labeling for collagen type IV along the margins of beams in the lamina cribrosa, due to accumulation of basement membrane-like materials. We also noted material in the pores of the laminar beams that labeled with antibodies to collagen types I, III and IV, but not elastin. In transected eyes, increased type IV labeling of laminar beam margins resulted solely from redundant astrocyte basement membranes. Extracellular matrix deposition within laminar pores was not observed following optic nerve transection; hence this may be a selective response to elevated intraocular pressure. This response may alter the biochemical composition of the lamina cribrosa and its function in patients with elevated intraocular pressure.