Diabetes mellitus is associated with a number of changes in the cornea. These include increased corneal autofluorescence, thickening and enhanced endothelial cell permeability. In this study we have investigated the biochemical changes of corneal collagen due to advanced Maillard reaction and lysyl oxidase mediated crosslinking in diabetes. Advanced Maillard reaction was estimated by collagen-bound fluorescence and pentosidine. Hydroxypyridinium (a trifunctional fluorescent crosslink) was estimated as an index of lysyl oxidase mediated crosslinking. Both fluorescence (p < 0.05) and pentosidine were present at higher levels in diabetic corneas when compared with age-matched control corneas. Hydroxypyridinium levels were only marginally increased in diabetes. These results suggest that corneal collagen is modified in diabetes by advanced Maillard reaction and that such modifications may have effect on corneal thickening, endothelial cell permeability and other abnormalities of the cornea in diabetes.