Cellular characteristics of KU-1 and KU-7 cells after a long term in culture were evaluated for eligibility of in vitro model of human transitional cell carcinoma of the urinary bladder. The KU-7 cells derived from superficial papillary tumor showed small, polygonal and homogeneous cells, while the KU-1 cells derived from a broad basic invasive carcinoma showed a variety in size as well as piling up tendency. The adhesiveness of these cells in culture was examined and a significant difference in their cellular structures, a thick multilayered mass in KU-1 while a thin flat spreading in KU-7, was found by each rotating culture and culture on collagen sponge matrix. KU-7 cells cultured without sera responded to transforming growth factor (TGF-alpha) but KU-1 cells did not show any response to the factor. These findings indicate that KU-7 and KU-1 cells have maintained some basic characteristics of papillary tumors and infiltrating carcinomas, respectively.