All whole eyes from patients with diabetes mellitus on file in the Laboratory of Oph thalmic Pathology at the Hospital of the University of Pennsylvania were reviewed, a total of 20, of which three were autopsy eyes. Hematoxylin-and eosin-stained sec tions were available through the axial por tions of the eye, including pupil and optic nerve, in all cases. Sections stained with both Best's carmine method for glycogen and the periodic acid-Schiff (PAS) reaction, with and without diastase, Masson's trichrome, Verhoeff-van Gieson elastic, toluidine blue, crystal violet, Alcian blue and col loidal iron, with and without hyaluronidase and/or diastase, oil red-O on frozen sections and Prussian blue were available in selected cases. Serial sections were performed on the entire axial portion of three eyes. In addi tion, trypsin-digested retinas were available for study from the posterior halves of 12