DNA ploidy patterns in six cases of scirrhous gastric carcinoma were examined by scanning cytophotometry, using 15 micron paraffin sections which were confirmed to involve a single whole nucleus. Measurements of DNA content were performed in 70 to 100 cancer cells each in intramucosal (m), submucosal (sm), propria muscular (pm) and subserosal (ss) parts of the tumor. Out of the six scirrhous gastric carcinomas, four were generalized ones and two were localized ones. Aneuploidy with diploid stem line (mosaic pattern) was seen in two cases (generalized type). The remaining four cases (two cases of localized type and two cases of generalized type) were composed of a diploid stem cell line with or without polyploid cells. Stem cell line did not change through the gastric wall, but in three cases (one diploid case and two mosaic cases), the number of polyploid or aneuploid cells significantly increased at the deep infiltrative site. These findings suggest that DNA ploidy of scirrhous gastric carcinoma is determined at an early stage of tumor proliferation and that the increase of polyploid cells and aneuploid cells in the deeper layer might participate in tumor progression. Moreover, there was no evident correlation between the increase of polyploid or aneuploid cells and the expression of oncogene products or EGF related growth factors.