Two cell lines derived from primary human renal-cell cancers (RCC) have been established and characterized. Cell line 786-O has been in culture for longer than 1 year and has been subcultured more than 50 times. It has a doubling time of 45 hr and a hypertriploid karyotype and possesses a Y chromosome. Cell line 769-P also has been in culture for longer than 1 year. It has been subcultured 50 times and has a doubling time of 35 hr and a hypodiploid karyotype. Cells from both lines are epithelial, and they produce tumors in the cheek pouches of immunosuppressed hamsters. Neither cell line is contaminated with Mycoplasma. Cells of the two lines can be distinguished from HeLa cells both by their karyotypes and by the mobility patterns of their isoenzymes of glucose-6-phosphate dehydrogenase.