Correlation between nuclear DNA content of tumor cells and survival, pathologic findings, as well as family history of patients was studied using paraffin-embedded materials from 85 cases of esophageal cancer and 52 cases of colorectal cancer. Nuclei were isolated from paraffin sections by the method of Hedley et al. and stained with propidium iodide. DNA index was calculated using nuclear DNA content of lymphocyte from the same patients as the external standard. Distribution of DNA indices showed a single peak in esophageal cancer, while it was bimodal in colorectal cancers. In esophageal cancers, although there was a significant correlation between survival and depth of invasion or nodal involvement, there was a very weak correlation between survival and DNA aneuploidy. Only for advanced cases, the patients who had tumors with diploidy or low ploid aneuploidy lived significantly longer than those with high ploid aneuploidy. On the other hand, in regard to colorectal cancers, the patients who had tumors with diploidy survived significantly longer than those with aneuploidy. Furthermore, patients who showed higher degree of aneuploidy tended to have poorer prognosis. There were no correlations between DNA ploidy and histologic type, depth of invasion, nodal metastasis, stage or family history of cancer.