A new ovarian cancer cell line has been established from the dispersed cells taken from a heterotransplanted tumor at the 6th passage in nude mice which had been serially transplanted with a primary lesion of undifferentiated carcinoma (FIGO) of the ovary. Selection of cancerous epithelioid cells was completed by the 4th passage by means of the colonial cloning method. The cell line designated TYK-nu was subcultured serially in Eagle's MEM with 10% FCS more than 100 times over 31 months at March, 1986 and was observed to produce a tumor on implantation into nude mice histologically similar to the original tumor. These cells form a monolayer in a pavement-like arrangement with polygonal cells including giant cells and reveal a lack of contact inhibition. PAS positive substance can be seen in the cytoplasm. Desmosome structure, well-developed cell organelles and glycogen granules can be found by electron microscopy. The population doubling time was about 37 hours and the plating efficiency was 13-17%. All cells were seen to be of the human karyotype on chromosomal analysis and the number of chromosome in the majority of cells was hyperdiploidy with a mode of 56 at the 6th and 84th passages. A submetacentric marker chromosome was present. Using in vitro colony assay, TYK-nu was studied for drug sensitivity to cisplatin, adriamycin, vincristine, 5-fluorouracil and etoposide, and found to be sensitive to cisplatin.