With age human collagen demonstrates, amongst other changes, reductions in solubility, elasticity and permeability. Many of these changes have been attributed to non-enzymic glycosylation (glycation)-a spontaneous addition of sugar molecules to any protein with free amino groups. The resulting formation and accumulation of Advanced Glycation End-products, some of which may be cross-links, has been shown in both long- and short-lived proteins. We have shown that glycation of human corneal and scleral collagen increases with age and that this is accompanied by increases in cross-linking and collagen intermolecular spacing. We have now investigated several compounds that have been used to inhibit glycation, including aspirin, and have shown that all the inhibitors also prevent the increase in intermolecular spacing caused by glycation.