Proteoglycans are important constituents of all connective tissues. Together with collagen, they provide the structure and mass of the extracellular matrix and contribute to the physical and mechanical properties of the tissues. The cornea of the eye has the special requirement of transparency, and proteoglycans may well maintain the regularity of collagen fiber spacing that is essential for this property. Methods are now available for the extraction and fractionation of the proteoglycans of the corneal stroma. In addition, the cornea can be maintained for long periods in organ culture with no apparent deterioration. The cornea thus offers an ideal undisturbed system in which to measure relative rates of synthesis and degradation of the carbohydrate and protein portions of the proteoglycan molecules. Intact rabbit corneas will be cultured in the presence of various isotopically labeled precursors. The cell layers will be removed and the stroma extracted for the fractionation of proteoglycans. The rate of isotope incorporation into the keratan-sulfate-rich proteoglycans and other defined fractions of proteoglycans will be measured, and relative rates of synthesis of carbohydrate and protein components will be calculated. Similar experiments can be done on cornea from which the epithelium or the endothelium has been removed in order to evaluate the function of these tissues in the overall metabolism of the cornea. By use of "pulse-chase" labeling experiments, the turnover of the various proteoglycan components can be evaluated as an initial approach to an understanding of how the cornea maintains its integrity and function.