The distribution of calcitonin gene-related peptide-immunoreactive nerve fibers in the renal pelvis and ureter was examined by immunohistochemistry using whole-mount preparations and cryostat sections. The patterns of innervation were contrasted between the pelvis and ureter; the immunoreactive nerve fibers in the pelvis ran parallel to the long axis of each of the circular and longitudinal muscle layers, causing a lattice-like appearance of the nerve fibers. In the ureter, the immunoreactive fibers were accumulated in the subepithelial region and the longitudinal muscle. In both the pelvis and ureter, a portion of the nerve fibers of smaller caliber showed a swollen or beaded structure; they were located in the musculature and beneath the epithelium extending for considerable distances. Ligation of the ureter caused a marked decrease in the immunoreactive nerves in the pelvis and the proximal portion of the ureter, suggesting that the axonal flow in the calcitonin gene-related peptide-containing neurons of the ureter runs towards the pelvis.