We are using the heterotopic urinary bladder model (Cancer Research, 34: 2773, 1974) to study the transplantation, heterotopic growth, and fate of normal uroepithelium, of uroepithelium rendered abnormal by prior treatment of the donor with chemical carcinogens, and of transplantable invasive bladder cancer R 4909. In particular we will study and compare the evolution of bladder disease produced in situ with chemical carcinogens with its evolution as the lining of a transplanted heterotopic bladder, outside of the urinary stream. BIBLIOGRAPHIC REFERENCES: Toyoshima, K., Abaza, N., and Leighton, J. Histologic Comparison of the Growth of Rat Bladder Carcinoma R 4909 Observed for Two years in Vitro and Vivo. Cancer Research, 36: 2795-2799, 1976. Toyoshima, K., Valentich, J., Tchao, R., and Leighton, J. Conditions of Cultivation Required for the Formation of Hemicysts in Vitro by Rat Bladder Carcinoma R 4909. Cancer Research, 36: 2800-2806, 1976.