An ultrastructural study of the sympathetic ganglia, dorsal sympathetic chain, and Auerbach's plexus is described in the streptozotocin diabetic rat. The observations cover the first six weeks following induction of diabetes. Degenerative changes began to appear in the axonal plasma membranes and axoplasm of unmyelinated fibers at 24 hours and were widespread by two weeks. Axonal sprouting and regenerating axons began to appear and increase in number through the 6th week. Chromatolysis in ganglion cells in sympathetic ganglia became apparent by two weeks as did degenerative changes in axons of Auerbach's plexus. This somewhat later appearance of changes in ganglion cells and Auerbach's plexus suggested the primary changes occurred in the postganglionic fibers. The cycle of change from degeneration to regeneration in the areas examined suggests either a possible toxic effect of streptozotocin or a combination of metabolic disturbances as a cause of this neuropathy.