The structure of the lamina cribrosa was studied by histological and immunocytochemical techniques and by scanning and transmission electron microscopy in four eyes removed surgically and in 21 normal eyes obtained from an eye bank. Dissection of the eyes emphasised the relatively fragile links between lamina and sclera. Reticulin staining of the fibrous trabeculae in the posterior (scleral) part of the lamina revealed a structure composed of interweaving skeins of collagen fibres frequently arranged tangentially around the canals, 40-220 microns in diameter, through which optic nerve axons pass. Immunocytochemistry for glial fibrillary acidic protein demonstrated the intimate web that astrocyte processes form around axons within the canals of the lamina and the close association of astrocyte processes and fibrous trabeculae in the posterior part of the lamina. Scanning electron microscopy clearly demonstrated anatomical relationships of the lamina cribrosa and the wide variation in the size of the canals in the lamina. Transmission electron microscopy confirmed the close association of astrocyte processes with axons demonstrated in the immunocytochemical preparations. The results of this study emphasise the complex relationships between astrocytic, neural and fibrous elements in the lamina cribrosa and how more information is required regarding the mechanical and metabolic properties of the astrocyte web and the fibrous trabeculae before the role of the lamina cribrosa in the pathogenesis of nerve damage in glaucoma can be fully assessed.