Tissue from 53 human eyes was used for qualitative and quantitative morphological study (light microscopy and electron microscopy) of age-related changes in the human outflow apparatus. The specimen source was surgical procedures. Qualitative observations showed that the general configuration of the trabecular meshwork changed gradually with age, from a long wedge shape to a shorter, more rhomboidal form. The scleral spur became more prominent, the uveal meshwork more compact, and localized canal closure increased in incidence. Intercellular cytoplasmic processes between neighboring trabecular endothelial cells were less evident and areas of trabecular denudation were frequently observed in older eyes. Quantitative light microscopic studies showed a progressive thickening of the trabeculae, and the numbers of giant vacuoles in the lining endothelium of Schlemm's canal decreasing significantly with age. Morphometric analysis of the cribriform layer (transmission electron microscopy) showed that there was a change in the character of the extracellular materials with an increase in the deposition of electron dense plaques and a decrease in the ground substances from the fifth decade onwards.