Three transitional cell carcinomas induced in Fischer 344 rats by a methylcholanthrene pellet or a foreign body inserted locally into the bladder were serially transplanted in the syngeneic strain for up to 6.5 yr. There were no changes in the individual morphological characteristics of the tumors during this time. Cells cultured in vitro for varying numbers of passages reproduce regularly the morphology of each tumor when they are injected back into the animals, and results from a microcytotoxicity assay for cellular immunity indicate that they retain a common bladder tumor specific antigen. These tumors are useful for research in tumor biology and are offered to other scientists seeking transplantable carcinomas for experimentation.