This study was carried out to investigate whether there is any difference of biological characteristics between a gastric cancer cell line (KATOIII) and another cell line derived from liver metastasis of the same cell line (KATOIII-H2). The liver metastasis was produced by intrasplenic injection of the fluid containing of KATOIII in nude mouse and new cell line was established using the cells of metastatic site. The results are as follows. 1) Inoculation of KATOIII-H2 into the spleen produced liver metastases in all of the experimental animals, whereas the same procedure with KATOIII produced metastasis only in 30% of the animals. 2) KATOIII-H2 exhibited more prominent platelet-aggregating activity than KATOIII. 3) There is no difference between two cell lines on doubling time, histological findings of the xenografts and chromosomal number. 4) DNA index of KATOIII-H2 is lower than KATOIII and the trisomy in NO. 20 chromosome of KATOIII-H2 was noted. The results indicate that metastatic potential is different between two cell lines and this fact is probably in a part because of the different platelet-aggregating activity of each cell line.