Obtain viable normal dissue, with intact urothelium supported by mesenchyme, from human bladders, normally by transurethral biopsy of patients being examined for suspected urinary tract disease, but occasionally from cystectomy specimens freshly removed in the course of treatment. Establish long-term in vitro organ cultures of such normal human bladder explants, and to establish cell cultures in parallel, if possible. Determine the parameters for normal growth of human urothelium in vitro in organ culture by comparison with parameters already established for rat bladder explants in vitro, and rat and human bladder in vivo. Apply methods of experimental carcinogenesis, already developed in vivo and in vitro for the rat, to the induction of carcinogenesis in human bladder explants cultured in vitro and to study the changes in the parameters as established above.