Implantation of normal bladder mucosa beneath the kidney capsule of a syngeneic animal, results in a heterotopic bladder lined by a one to three cell layer of urothelium. This cystic structure can be maintained for greater than 90 days and displays many of the differentiation characteristics of a normal bladder, both at the light and electron microscopy level. Preneoplastic urothelial cells behave in a similar manner recreating a heterotopic bladder lined by urothelium displaying aberrant differentiation and surface morphology. All tumorigenic cell lines tested in this model produced solid tumor growth within a few weeks. The subrenal capsule represents an alternative site for the reconstitution of urothelial material at different stages of neoplastic progression.