A cell line derived from a poorly differentiated transitional cell carcinoma of the bladder in a patient previously treated with external beam radiation has been established. The line has stable hyperdiploid karyotype which is distinct from other established transitional cell carcinoma lines. Injection of the cells into nude mice induces tumor with histological characteristics similar to the original tumor. This line may serve as a model to study mechanisms of radioresistance in transitional cell carcinoma of the urinary bladder.