Epidermal growth factor (EGF) concentration in urine was measured with a radioimmunoassay in 40 untreated patients with urothelial tumors and a comparable control group of 25 normals. The concentration of EGF in urine from the patients with bladder, renal pelvic or ureter tumors was lower than normal (p < 0.05). Patients with T4 tumors had lower concentrations of EGF compared with those of other stages. EGF concentrations after transurethral resection of bladder tumors were significantly elevated compared with the values before operation. These findings suggest that urothelial tumors are related to a low concentration of EGF and that a decrease of EGF is associated with invasion of tumors.