Morphometric measurements of epithelial adhesion structures were performed on electron micrographs of corneas of diabetic patients (ages 35 to 77 years) and controls of similar age (ages 21 to 79 years). Penetration of the anchoring fibrils from the deepest layer of the basal lamina into the stroma was significantly decreased in diabetics (0.41 +/- 0.02 microns) compared with controls of similar ages (0.65 +/- 0.03 microns). Significant thickening of the basal lamina in diabetics (50.1 +/- 7.6 microns 2/100 microns basal cell membrane) was noted compared with controls (32.0 +/- 6.3 microns 2/100 microns), but no significant differences were noted in the percentage of the basal cell membrane occupied by hemidesmosomes. Decreased penetration of the anchoring fibrils into the stroma may cause the loose adhesion between the stroma and basement membrane observed in diabetes.