Quick-freeze, deep-etch method was used to study the ultrastructure of normal monkey optic nerve lamina cribrosa. Glial cell somata were located beside collagen fibril bundles in the lamina cribrosa. Glial intermediate filaments, which were the main cytoskeletal proteins of 10-12 nm in diameter, were loosely packed in the somata and were tightly stacked in the processes. The glial plasma membrane directly abutted onto the myelin sheath of the optic nerve axon. The main component of the extracellular matrix (ECM) in the lamina cribrosa was interstitial collagen fibers of 30-60 nm in diameter, which were bridged by processes 5 nm in diameter and 20-30 nm in length and by 5 nm wide mesh-like structures. Small vessels running in the laminar beams were totally surrounded by basement membranes, laminar ECM, and glial cell components and thus were separated from optic nerve axons. The basement membrane which surrounded the laminar ECM was a fine fibrillar structure of 5 nm in diameter and also had numerous fibrils anchoring it to plasma membranes of vascular pericytes and glial cells.