To estimate autonomic neuropathy in the spontaneously diabetic Chinese hamster, which is an established strain for the non-obese non-insulin-dependent diabetes mellitus model, gastric emptying and morphometric analysis of the vagus nerve were studied in 12-month-old spontaneously diabetic Chinese hamsters (duration of diabetes was 9 months). Gastric emptying was determined by the phenol red method. Vagus was obtained from just above the diaphragm. Morphometric analysis of myelinated fibers was performed light-microscopically using semi-thin sections and unmyelinated fibers were studied electron-microscopically using ultra-thin sections. Gastric emptying of spontaneously diabetic Chinese hamster was significantly increased compared with control (86.6 +/- 1.9 vs. 51.2 +/- 3.4, P < 0.01). Myelinated fibers of the spontaneously diabetic Chinese hamster were not different from control animals, while the size of unmyelinated fibers in the spontaneously diabetic Chinese hamster was significantly decreased. These data suggest that pathological changes in unmyelinated fibers, which consist mainly of afferent fibers, might play a role in gastric motor dysfunction in the spontaneously diabetic Chinese hamster.