A simple method for the harvest of bladder cell types from surgical specimens was used to generate strains of normal human urothelial cells that could be reproducibly cultivated, passaged and extensively expanded in serum-free medium. Immunostaining of the bladder epithelial cells with broadly reacting anti-cytokeratin antibodies and with an anti-cytokeratin antibody specific to cytokeratin 7, a transitional cell marker, indicated that they expressed a stable epithelial phenotype with serial passage. Low levels of immunostaining for E-cadherin and low levels of E-cadherin messenger ribonucleic acid, as determined by Northern blot analysis, and strongly positive immunostaining with an anti-vimentin antibody indicated collectively that the uroepithelial cells express a nonbarrier-forming phenotype under these culture conditions. However, when the urothelial cells were implanted subcutaneously into athymic mice on biodegradable synthetic polymers, they formed multilayered structures, suggesting that they retain the capability to differentiate in a living host. The urothelial cells proliferated in an epidermal growth factor independent manner and expressed high levels of transforming growth factor-alpha and amphiregulin messanger ribonucleic acids, suggesting the possibility of autocrine regulation of growth by epidermal growth factor-like factors. Cytogenetic analysis indicated that urothelial cells cultured for 6 passages possessed a normal chromosomal complement. These results demonstrate that primary cultures of autologous human bladder epithelial cells can be extensively expanded in vitro and, consequently, might be used in cell transplantation strategies for genitourinary reconstruction.