The relationship between DNA ploidy and effects of preoperative hyperthermo-chemo-radiotherapy were investigated in 118 patients who underwent esophageal resection and reconstruction for carcinoma of the esophagus, including 56 treated with hyperthermo-chemo-radiotherapy (HCR therapy) and 62 treated with chemo-radiotherapy (CR therapy). DNA ploidy patterns were grouped into low and high ploidies, according to the degree of dispersion and the peak value on the DNA histogram. In the low ploidy group, there were no significant differences in the prognosis and histologic effects between the HCR and CR therapies. In the high ploidy group, however, the difference in survival curves was statistically significant, the 3-year survival rates of patients given HCR therapy and CR therapy being 26.7% and 10.7%, respectively (P less than 0.05). The HCR therapy increased the rate of "markedly effective" in the resected tissue compared with findings in cases of CR therapy. These findings show the positive effects of the HCR therapy for carcinoma of the esophagus, especially for patients with an aneuploid profile and a poor prognosis.