1) For past 10 years, 11 epithelial liver cell lines from baby rats of Donryu strain have been established in our laboratory. 2) All cultured cells in the 11 cell lines showed the same epithelial morphology in early culture passages irrespective of culture methods. 3) The cultured cells progressively deviated from normal to abnormal with time in chromosome as well as in morphology during long-term cultivation; normal diploid cells shifted to aneuploid and also homogeneous epithelial cells changed to heterogeneous in shape. 4) The cells in all of the 11 cell lines eventually underwent spontaneous malignant
transformation in vitro after about 600 culture days and produced tumors in syngeneic newbown rats about 300 days after inoculation. 5) Histology of tumors showed mainly hepatocarcinomas and a few sarcomatous figures. 6) Chromosome numbers of the cultured cells in the 11 cell lines were in the near-diploid range in six of them and in the hypertriploid to hypotetraploid range in the remaining five, when chromosome analysis was done at the time of malignant transformation in vitro.