A cell line derived from a well-differentiated human transitional cell carcinoma of the urinary bladder, designated TSGH-8301, was established in vitro. The cultured epithelioid cells exhibited monolayer growth and loss of contact inhibition. The tumorigenicity of TSGH-8301 had been shown by growth in soft agar and tumor induction in athymic nude mice. A reverse ratio of lactate dehydrogenase (LHD) isoenzyme in the cell line and nude mouse-grown tumors was seen predominantly with LDH-V. Chromosomal analysis revealed a heterodiploid stem line with a modal number of 50. Sera of urinary bladder cancer patients reacted with membrane antigens of the TSGH-8301 cells, suggesting the existence of tumor-associated antigens in the cells. In vitro chemosensitivity tests of these cells may provide data valuable in the selection of proper anticancer drugs for the TSGH-8301 donor patient.