Monoclonal antibody 425, which binds to an extracellular domain of the epidermal growth factor receptor, was used to evaluate the expression of this antigen on bladder cancer cells. Epidermal growth factor receptor was found on all bladder cancer cell lines tested. Immunoperoxidase staining of fourteen invasive human bladder cancers with monoclonal antibody 425 demonstrated that ten showed strong staining, one showed weak staining and three were negative. Five noninvasive tumors were similarly examined. Four of these were negative and one showed weak staining. Biodistribution experiments with human bladder tumor xenografts in athymic nude mice using radiolabeled monoclonal antibody 425 and an isotype matched control antibody demonstrated specific tumor localization at five and seven days following antibody injection. Successful imaging of a human bladder tumor xenograft was achieved five days post antibody injection. These data confirm that epidermal growth factor receptor expression correlates with bladder cancer stage and suggests that epidermal growth factor receptor may serve as a target antigen for radioimmunoscintigraphy.