The ultrastructure of the normal rat ureter has been studied in order to correlate the morphological findings with the function of the organ. Electron microscopy demonstrates that the ureteral musculature behaves as a functional syncytium which permits the spread of electrical excitation from cell to cell. A scanty number of nerve endings without evidence of autonomic ganglia was found throughout the ureteral layers. These morphological data support the hypothesis that ureteral peristalsis is an essentially myogenic phenomenon, the influence of the autonomic nerve supply being limited to modulating peristalsis and influencing ureteral tonus.