Electron microscopic examination of peripheral nerves within dermal corium based upon skin biopsies (punch diameter = 6 mm) of chronic diabetic dogs and cats in comparison with normal controls revealed that more than 90% of the diabetic animals (31/34 dogs, 9/10 cats) had developed characteristic neuropathies. The main features were of axonal atrophy of myelinated and unmyelinated fibers, demyelination and - to a lesser degree - intraaxonal accumulation of glycogen (about 25%). In contrast with human diabetic polyneuropathy vascular basement membranes were throughout of normal appearance. Thickening of the perineural basement membranes were observed in a few canine cases only. Diagnostic procedures as well as questions on pathogenesis are discussed in detail.