The morphological changes in the inner surface of the human anterior chamber angle during pre and postnatal development were studied by light microscopy, scanning and transmission electron microscopy. Seventeen human foetal eyes (12-22 weeks) and ten infant and juvenile eyes (2.5 months--8 years) were investigated with the aim of establishing whether the trabecular meshwork is covered by an uninterrupted membrane at any stage in development. In 12-14 week old foetal eyes cuboidal corneal endothelial cells cover the inner surface of the anterior half to one third of the trabecular anlage. In this region there is a transition to more flattened uveal trabecular endothelial cells. Only rarely did corneal endothelial cells extend completely to the angle apex. The transition zone between corneal and uveal trabecular endothelial cells becomes located more anteriorly as development progresses. Intercellular gaps, which occur between uveal trabecular endothelial cells as early as 12-14 weeks in development, enlarge and become more frequent during development thus providing a route of communication between the anterior chamber and the developing intertrabecular spaces or channels. In the first months of life only a few cord-like uveal trabeculae orientated predominantly in a meridional direction overlie the more lamellate corneoscleral trabeculae. By the second year typical uveal trabeculae are more prominent and form a web-like arrangement. This is accompanied by a gradual decrease in the frequency of the cytoplasmic extensions of uveal trabecular endothelial cells which circumscribe the intratrabecular gaps. The timing of this remodelling and maturation appears to be remarkably variable between individuals. The implications of these findings on the theories of the pathogenesis of congenital glaucoma are discussed.