Epidermal growth factor (EGF) is excreted in urine in high concentrations in a biologically active form. Several lines of evidence indicate that EGF plays a role in transitional cell carcinoma (TCC) development and growth. These include: (1) EGF in the normal urine of rats promotes chemically initiated TCC; (2) EGF in normal human urine stimulates the clonal growth of human TCC cells in vitro; (3) EGF stimulates the in vitro growth of human TCC cells, but not normal human urothelial cells; (4) the density and distribution of the EGF receptor (EGF-R) on human urothelial tissues permits significant access of premalignant, dysplastic, and malignant cells to EGF; and (5) the concentration of EGF in the voided urine of patients with TCC is reduced, implying that EGF may be "extracted" from urine by the greater number of EGF-Rs in patients with urothelial malignancy. Abnormal expression of the urothelial EGF-R and/or altered excretion of EGF may well precede overt evidence of TCC and thus may serve as markers of risk or exposure. Similarly, reversion of EGF-R expression or the return of excreted EGF to normal levels may provide a marker of response for preventive and therapeutic strategies. Interference with the EGF/EGF-R interaction through dietary or pharmacological manipulations of the urine, or via targeting strategies employing intravesical administration of conjugated toxins or isotopes is already being employed in experimental and clinical studies. These approaches offer promising new tools in the detection, monitoring, prevention, and management of early stage bladder cancer.