The relationship of DNA ploidy to clinical, pathological or prognostic data was investigated in 70 surgically removed gastric cancers, 60 of which were advanced cases. The cellular DNA content was measured by means of flow cytometry. Overall, DNA aneuploidy was seen in 43 of the cases (61%) while the normal gastric mucosa consisted of only a diploid line without any aneuploid population. Ploidy levels of gastric cancer spanned a wide range from a hypodiploid value to a hyperpentaploid value, although near-diploid and near-triploid cases were the majority in the series. No significant association between ploidy and either age or sex was found. The incidence of DNA aneuploidy was significantly higher in differentiated adenocarcinomas than in undifferentiated ones (p less than 0.05). However, DNA ploidy was not related to some pathologic characteristics such as the extent of tumor invasion and the frequency of lymph node metastasis. According to Kaplan-Meier survival plots, prognosis of the patients with DNA diploid tumors tended to be better than that of aneuploid tumors, but the difference was not statistically significant.